LIBRARY 


ELECTROCHEMISTRY 


OF 


ORGANIC    COMPOUNDS 


BY 

DR.  WALTHEK   LOB 
t ' 

Privatdocent  in  the  University  of  Bonn 


AUTHORIZED  TRANSLATION  FROM  THE  AUTHOR'S  ENLARGED  AND 
REVISED  THIRD  EDITION 


ELECTROLYSIS  AND  ELECTROSYNTHESIS 

OF 

ORGANIC    COMPOUNDS 

BY 

H.    W.    F.    LORENZ,    A.M.,    PH.D. 

Graduate  of  the  University  of  Berlin 

Formerly  Instructor  of  Organic  Chemistry  in  the  University  of  Pennsylvania 
Translator  of  Lassar-Cohrfs  "Urinary  Analysis,"  etc. 

WITH   TEN   ILLUSTRATIONS 


FIRST    EDITION 

,      ^       FIRST   THOUSAND 
OF  "THE 

UNIVERSITY 

OF 

•fiammife       NEW  YORK 

JOHN  WILEY    &  SONS 
LONDON:  CHAPMAN   &   HALL,  LIMITED 

1906 


CROXER 

f* 


Copyright,  1905 

BY 
H.    W.    F.    LORENZ 

BIOLOGY 
LIBRARY 


, 

' 


8JOLOGY 
LIBRARY 


ROBERT  DRUMMOND,   PRINTER,   NEW  YORK 


AUTHOR'S  PREFACE  TO  THE  THIRD 
GERMAN  EDITION. 


THE  great  progress  which  the  electrochemistry  of  organic 
compounds  has  made  in  the  past  few  years  rendered  it  desirable 
to  rearrange  the  whole  material,  and  to  express  by  a  suitable 
title  the  extension  of  the  task  which  the  book  seeks  to  fulfil. 

The  theoretical  discussions  which  form  an  introduction  to 
the  experimental  part  of  electrolysis  are  of  a  subjective,  par- 
tially hypothetical  character,  that  the  present  state  of  our 
knowledge  of  the  mechanism  of  the  electrical  reaction  cannot 
prevent  from  being  otherwise.  But  the  given  ideas  have  proved 
trustworthy  as  aids  in  directing  and  arranging  my  experimental 
work;  perhaps  they  will  be  equally  serviceable  to  others,  not- 
withstanding ,  the  possibility  and  justifiability  of  divergent 
views. 

The  object  of  the  work  has  remained  the  same  in  the  new 
as  in  the  old  form:  to  give  a  connected  survey  of  what  has 
been  done,  and  to  incite  to  further  efforts  in  investigations. 

I  desire  here  to  express  my  thanks  to  Dr.  E.  Goecke  who 
helped  me  in  looking  over  the  literature  on  the  subject. 

The  second  English  edition,  corresponding  to  the  present 
German  edition,  will  appear  shortly. 

WALTHER  LOB. 

BONN,  April,  1905. 


155633 


TRANSLATOR'S  PREFACE  TO  SECOND 
AMERICAN  EDITION. 


A  NEW  edition  of  Doctor  Lob's  book  on  this  interesting 
and  important  subject  has  become  necessary,  because  of  the 
great  increase  in  the  past  few  years  in  the  quantity  of  new 
experimental  material.  The  author  has  happily  met  this 
requirement  in  his  present  excellent  work  on  the  "  Electro- 
chemistry of  Organic  Compounds."  Doctor  Lob  has  spared 
no  pains  to  bring  the  subject-matter  strictly  up  to  date,  and 
has  entirely  rewritten  and  rearranged  the  material  so  as  to 
present  it  in  the  best  possible  form. 

Two  special  chapters  have  been  arranged,  devoted  to  a 
more  thorough  discussion  of  the  theoretics  and  methodics  of 
organic  electrochemistry,  and  also  a  chapter  on  electric  en- 
dosmose.  The  whole  of  Part  II,  on  electrothermic  processes 
and  the  silent  electric  discharge,  is  new. 

Complying  with  the  wish  of  the  author  in  this  as  in  the 
first  translation,  the  original  text  has  been  followed  by  the 
translator  as  closely  as  possible. 

It  is  hoped  that  this  new  edition  will  meet  with  the  same 
cordial  reception  accorded  the  earlier  one. 

SPRINGFIELD,  OHIO,  October,  1905. 


CONTENTS. 


PAGE 

INTRODUCTION 1 


PART  I. 
ELECTROLYTIC  PROCESSES. 


CHAPTER  I. 

THEORETICS 5 

1.  Forms  of  Reaction 5 

2.  Properties  of  Electrolytic  Processes 10 

3.  Significance  of  the  Velocity  of  Reaction 11 

4.  Reaction  Velocity  and  Specific  Effect  of  Reducers^and  Oxidizers .  13 

5.  Electrode  Potential  and  Reaction  Mechanism 14 

6.  Electrode  Processes 18 

A.  Cathodic  Processes 18 

a.  Unattackable  and  Attackable  Cathodes 18 

b.  Excess  Potential  and  the  Reduction  Action 20 

c.  Concerning  Substances  Reducible  with  Difficulty 23 

B.  Anodic  Processes 27 

7.  Theory  of  the  Reaction  Velocity  in  Electrolytic  Processes 30 

a.  Diffusion  Theory 30 

b.  Osmotic  Theory  of  Electrical  Reduction 34 

c.  Summary  of  the  Theories 37 


CHAPTER  II. 

METHODICS 40 

1.  The  Cells 40 

2.  Arrangement  of  Experiments  and  Measurements  of  Potential. ...  44 

3.  The  Electrodes 51 

vii 


viii  CONTENTS. 


CHAPTER  III. 

PACK 

ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS 54 

1.  Carbon  and  Hydrocarbons 54 

2.  Nitro-derivatives  of  Hydrocarbons 56 

3.  Hydroxyl  Compounds 57 

4.  Derivatives  of  the  Alcohols 65 

5.  Aldehydes,  Ketones,  and  their  Derivatives 66 

a.  Aldehydes 66 

b.  Ketones 69 

6.  Acids 75 

I.  Monobasic  Acids,  CnH2nO2 77 

II.  Monobasic  Alcohol-  and  Ketonic  Acids 95 

a.  Alcohol-acids 95 

b.  Ketonic  Acids 99 

III.  Dibasic  Acids 102 

IV.  Unsaturated  Dibasic  Acids 115 

V.  Polybasic  Acids 116 

7.  Amines,  Acid  Amides,  Imides  and  Nitriles 118 

8.  Carbonic-acid  Derivatives 121 

9.  Sulphur  Derivatives  of  Carbonic  Acid 130 


CHAPTER  IV. 

ELECTROLYSIS  OF  AROMATIC  COMPOUNDS 132 

1.  Hydrocarbons 133 

2.  Nitro-  and  Nitroso-compounds 135 

a.  General   Observations   on    the   Reduction   of    Nitro-Com- 

pounds 136 

b.  Reduction  of  Nitrobenzene 145 

I.  Chemical  Relations 145 

II.  Significance'-of  the  Electrical  Relations 149 

III.  Presentation  of  the  Reduction  Phases  of  Nitrobenzene  154 

c.  Substitution  Products  of  Nitrobenzene 163 

I.  General  Laws  Governing  Substitution 163 

II.  Homologues  of  Nitrobenzene 168 

III.  Halogen  Derivatives  of  Mononitro-bodies 174 

IV.  Nitrophenols 175 

V.  Nitranilines 177 

VI.  Nitro-derivatives  of  Diphenylamine  and  of  Amidotri- 

phenylmethane 180 

VII.  Nitroaldehydes  and  Nitroketones 181 

VIII.  Nitrobenzene-carboxylic  Acids 183 

IX.  Nitrobenzene-sulphonic  Acids 186 

X.  Further  Reductions  of  Nitro-bodies 188 


CONTENTS.  ix 

PAGE 

XI.  Nitro-derivatives  of  the  Naphthalene-,  Anthracene-, 

and  Phenanthrene  Series. 190 

XII.  Nitroso-  and  Nitro-derivatives  of  the  Pyridine  and 

Quinoline  Series 192 

3.  Amido-derivatives 193 

4.  Phenols 199 

5.  Alcohols,  Aldehydes,  Ketones,  Quinones 202 

6.  Acids 211 

7.  Acid  Amides  and  Nitriles 215 

8.  The  Reduction  of  Indigo 216 

9.  Pyridine  Derivatives  and  Alkaloids 217 

10.  The  Camphor  Group 225 

11.  Electrolysis  of  Blood  and  Albumen 229 

CHAPTER  V. 
ELECTROLYSIS  WITH  ALTERNATING  CURRENTS 230 

CHAPTER  VI. 
ELECTRIC  ENDOSMOSE 233 


PART  II. 

ELECTROTHERMIC  PROCESSES  AND  THE  SILENT  ELECTRIC 

DISCHARGE. 


CHAPTER  I. 

THEORETICS  AND  METHODICS 235 

1.  Theoretics 235 

2.  The  Reaction  Temperatures 238 

3.  Arrangements 241 

CHAPTER  II. 

THE  SPARK  DISCHARGE  AND  THE  VOLTAIC  ARC 244 

1.  The  Spark  Discharge 244 

2.  The  Voltaic  Arc 249 

CHAPTER  III. 
THE  UTILIZATION  OP  CURRENT  HEAT  IN  SOLID  CONDUCTORS 252 


X  CONTENTS. 

CHAPTER  IV. 

PAGE 

THE  SILENT  ELECTRIC  DISCHARGE  AND  THE  EFFECT  OF  TESLA-CURRENTS  .  261 

1.  The  Silent  Electric  Discharge 261 

a.  Arrangements ; 263 

b.  Chemical  Results 265 

I.  Carbonic  Acid  and  Carbon  Monoxide 266 

II.  Hydrocarbons 270 

III.  Alcohols 273 

IV.  Aldehydes  and  Ketones 276 

V.  Acids  and  Esters 277 

VI.  1.  Concerning  the  Binding  of  Nitrogen  to  Organic  Sub- 
stances   279 

2.  Behavior  of  Vapors  towards  Tesla-currents 288 

LIST  OF  AUTHORS 293 

INDEX .  297 


OF  THE 

UNIVERSITY 

OF 


ELECTROCHEMISTRY 

OF 

ORGANIC    COMPOUNDS 


INTRODUCTION. 

CHARACTERISTICS   AND    CLASSIFICATION    OF   THE 
SUBJECT-MATTER. 

THE  application  of  electrical  energy  for  effecting  organic 
reactions  was  tried  long  ago  and  in  the  most  various  ways. 
The  observations,  however,  were  at  first  few  in  number,  leading 
points  of  view  were  lacking,  and  the  results  were  incoherent 
and  often  contradictory.  A  definite  start  in  attacking  the 
many  problems  which  are  presented  by  organic  chemistry  was 
not  made  until  larger  electrical  equipments  were  introduced 
into  scientific  and  technical  enterprises.  For  about  a  decade 
organic  electrochemistry  has  been  undergoing  a  quiet  but 
steady  development. 

Electrical  energy  can  be  employed  directly  or  indirectly 
for  accomplishing  chemical  reactions — directly,  if  the  field 
traversed  by  the  current  is  of  an  electrolytic  nature ;  indirectly, 
if  a  transformation  of  electrical  energy  into  other  forms  takes 
place,  which — for  instance,  heat  or  light — can  bring  about 
chemical  phenomena  outside  of  the  current  field.  Both  utilizable 
forms  of  electricity  are  of  theoretical  and  practical  importance; 
the  former  in  electrolysis,  particularly  in  reduction,  oxidation 


2  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

and  substitution  reactions,  the  latter  in  pyrogenic  and  photo- 
chemical processes.  Another  kind  of  electrochemical  action, 
and  one  in  which  the  connection  between  electrical  work  and 
chemical  effect  is  still  hidden  in  obscurity,  is  the  glow,  or  silent 
discharge.  In  spite  of  the  few  facts  known  about  this  form 
of  electrical  energy,  it  can  be  claimed  positively  that  it  is  of 
fundamental  importance  in  the  synthesis  of  simple  organic 
bodies  and  is,  perhaps,  a  means  for  explaining  the  methods 
which  living  nature  employs  in  building  up  substances. 

A  survey  of  the  great  number  of  organic  electrochemical 
investigations  shows  a  very  unequal  distribution  of  scientific 
labor  among  the  separate  parts  of  the  extensive  domain.  The 
electrolytic  reactions  have  been  by  far  most  thoroughly  investi- 
gated, particularly  the  reduction  processes.  Oxidation  and 
substitution  reactions  have  more  rarely  been  the  subject  of 
successful  researches. 

Pyrogenic  decompositions  and  syntheses  of  organic  substances 
produced  by  the  induction  spark,  the  electric  arc,  or  highly 
heated  conductors  of  the  first  class  have  been  numerously 
mentioned.  However,  we  are  just  beginning  to  obtain  scientific 
results  in  this  line  of  work.  It  has  already  been  mentioned 
that  our  knowledge  of  the  action  of  the  glow  and  convective 
discharge  on  carbon  compounds  is  extremely  insignificant. 

The  varied  properties  of  organic  bodies  explain  this  unequal 
treatment  and  the  result.  The  reduction  of  carbon  compounds 
occurs  usually  at  certain  .reducible  groups  in  the  molecule  with- 
out destroying  this  latter.  The  whole  molecule  is  usually  exposed 
to  the  action  of  the  electrolytic  oxygen.  The  final  product  of 
a  reduction  is  closely  related  chemically  to  the  material  started 
out  with;  the  end  result  of  an  oxidation  is  often  the  complete 
combustion  of  the  molecule.  Quite  a  number  of  possibilities 
exist  between  a  slight  attack  by  oxygen  upon  and  the  complete 
destruction  of  a  compound  by  oxidation.  A  realization  of 
these,  if  at  all  possible,  depends  upon  most  painstaking  observa- 
tions of  fixed  experimental  conditions,  which  are  often  difficult 
to  determine.  Hence  oxidation  processes  are  much  more  com- 


INTRODUCTION.  3 

plicated  than  reduction  processes,  and  usually  less  profitable. 
These  same  points  of  view  also  apply  to  electrolytic  substitu- 
tion, which,  being  an  anodic  process,  is  often  only  with  difficulty 
protected  from  the  oxidizing  action  of  the  current. 

The  relatively  great  sensitiveness  of  most  carbon  compounds 
to  high  temperatures  confined  electrothermic  decompositions  and 
syntheses  of  organic  bodies  to  a  small  area,  so  long  as  the  heat 
was  derived  from  the  induction  spark,  or  the  electric  arc. 
Electrical  energy  has,  however,  proved  itself  a  convenient 
medium  for  investigating  the  behavior  of  sensitive  substances 
at  relatively  high  temperatures,  ever  since  metallic  wires,  or 
carbon  filaments,  have  been  used  as  sources  of  heat  which 
can  be  easily  regulated  by  increasing  or  decreasing  the  current 
pressure. 

The  properties  of  electric  energy  as  well  as  those  of  the 
carbon  compounds  require  special  forms  of  experiment  for 
organic  electrochemistry.  These  differ  entirely  from  the  purely 
chemical  art  of  experimentation,  i.e.,  partially  new  experi- 
mental methodics  are  necessary.  The  more  it  was  possible  to 
recognize  the  important  points  in  the  course  of  an  electro- 
chemical process  the  clearer  the  viewpoints  became  regarding 
the  choice  of  the  most  suitable  conditions  for  experiment. 
The  endeavor  theoretically  to  represent  and  unite  the  numerous 
observations  went  hand  in  hand  with  the  experimental  develop- 
ment. Theoretical  considerations  led  to  new  experimental 
conditions  and  new  problems.  The  theory  becomes  closely 
associated,  by  certain  requirements,  not  only  with  the  subject 
of  the  experiment  but  also  with  its  arrangement.  A  descrip- 
tion of  organic  electrochemistry  must  fully  recognize  theory 
and  methodics  as  well  as  the  chemical  results. 

Depending  upon  the  forms  in  which  electrical  energy  is 
employed  in  organic  chemistry,  we  can  distinguish  three 
processes,  electrolytic,  electrothermic,  and  electric-discharge 
reactions.  A  threefold  division  into  theory,  methodics  and 
experimental  results,  hence,  naturally  follows  for  the  disposi- 
tion of  each  of  the  three  resulting  chapters. 


4  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

It  may  be  remarked,  particularly  in  regard  to  the  description 
of  the  methods,  that  only  the  necessary  and  important  data 
are  mentioned  here.  The  author  does  not  intend  to  give  a 
practical  guide  for  making  experiments.  Only  original  investi- 
gations or  special  text-books  1  can  serve  such  a  purpose.  It  is 
the  object  of  the  respective  descriptions  in  this  book  to  dis- 
cuss the  general  principles  and  to  lead  the  reader  to  a  clear 
understanding  and  a  correct  interpretation  of  the  various 
methods. 

1  See,  for  instance,  Oettel,  Electrochemical  Experiments,  1897  (trans- 
lated by  E.F.  Smith);  also  Oettel,  Practical  Exercises  in  Electrochemistry, 
1897  (translated  by  E.  F.  Smith,  Phila.);  Elbs,  Experiments  for  the  Electro- 
lytical  Preparation  of  Chemical  Preparations,  Halle,  1902. 


PART  I. 

ELECTROLYTIC  PROCESSES. 


CHAPTER   I. 
THEORETICS. 

1.  FORMS  OF  REACTION. 

Two  possibilities  must  be  distinguished  in  the  electrolysis 
of  organic  bodies.  The  carbon  compound  is  either  an  electro- 
lyte, i.e.,  a  salt,  base,  or  acid,  or  it  is  a  non-electrolyte. 

In  the  first  case  the  compound  itself  furnishes  the  ions 
which  condition  the  conductivity.  The  work  of  electrolysis 
then  consists  in  the  transportation  of  these  ions  to  the  anode 
and  cathode,  and  it  is  a  secondary  question  whether  these 
ions  are  liberated  molecularly  or  atomically,  or  whether  they 
react  with  one  another,  or  with  the  substance  still  present  in 
the  solution,  or  with  the  solvent. 

Of  the  organic  ions  the  anions  are  almost  exclusively  taken 
into  consideration,  since  organic  cations,  like  the  organic 
ammonium  ions,  have  been  little  investigated  as  to  their 
behavior  in  electrolysis.  The  actual  liberation  of  the  ions  can- 
not be  observed,  because  when  deprived  of  their  electrical 
state  they  cannot  exist.  On  the  contrary,  the  anions  often 
react  with  one  another  after  their  discharge.  Thus  either  a 
union  of  several  anions  occurs  or,  far  of tener,  more  complicated 
transpositions  and  decompositions  accompany  these  reactions. 

5 


6  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

An  example  of  the  first  kind  of  decomposition  is  furnished 
by  the  electrolysis  of  potassium  xanthate  l  : 

2  C2H5OCSSK=2  C2H5OCSS'+2  K\ 
2  C2 


In  this  case  two  anions  unite  to  form  xanthic  disulphide.  On 
the  other  hand,  in  the  electrolysis  of  sodium  acetate,  the 
anions  are  united,  but  carbonic  acid  is  simultaneously  split  off: 

2CH3COO=C2H6+2C02. 

The  anions  of  the  fatty  acids  show  this  behavior  to  a  greater 
or  less  degree  under  certain  current  conditions. 

But  if  the  organic  compound  does  not  conduct  the  current, 
other  ions  must  be  present  for  accomplishing  the  electrolysis. 
For  this  purpose  usually  an  inorganic  acid,  base,  or  salt- 
corresponding  organic  compounds  can  of  course  also  be  used— 
is  dissolved  in  the  solution.  Then,  primarily,  the  passage  of 
the  current  does  not  at  all  affect  the  organic  non-electrolyte. 
Only  the  ions  are  driven  to  the  electrodes  where  they  can  dis- 
charge themselves.  At  the  instant,  however,  when  the  dis- 
charge occurs,  the  role  of  the  organic  body  begins.  If  it  can- 
not react  with  the  discharged  ions  it  remains  unchanged, 
and  is  not  affected  by  the  action  of  the  electrolysis.  This 
possibility  will  naturally  not  be  considered  in  the  present 
discussion.  The  fact  to  be  observed  is,  that  the  carbon  com- 
pound reacts  with  the  "discharged  ions  —  it  then  becomes  a 
depolarizer. 

Many  organic  acids,  bases,  and  salts  can  act  as  depolarizers 
when  ions  are  discharged  which  react  easily  with  them.  For 
example,  p-nitrobenzoic  acid  in  alkaline  solution  is  reduced 
smoothly  to  p-azobenzoic  acid.  The  sodium  ions  which  are 
discharged  react  so  rapidly  with  the  nitro-group  that  the 
nitrobenzoic  acid  does  not  behave  as  an  electrolyte  but  essen- 
tially as  a  depolarizer,  particularly  since  the  ions  of  the  sodium 

1  Schall,  Ztschr.  f.  Elektrochemie  3,  83  (1896). 


THEORETICS.  7 

hydroxide  solution  take  care  of  the  conductivity.  Organic  elec- 
trolytes can  also  furnish  the  ions  which  act  upon  an  organic 
depolarizer.  Thus,  if  an  acid  is  electrolyzed  in  absolute  alcohol 
an  ester  is  sometimes  formed : 

RCOO  +C2H5OH  =  RCOOC2H5 + OH. 

In  this  case  the  alcohol  is  at  the  same  time  a  solvent  and  a 
depolarizer. 

We  therefore  divide  the  phenomena  of  electrolysis  of  carbon 
compounds  into  two  classes:  Either  the  organic  bodies  them- 
selves act  as  electrolytes — the  effect  of  the  electrolysis  is  the 
discharge  and  the  eventual  additional  reaction  of  their  ions  at 
the  electrodes  (primary  reactions) — or  they  are  depolarizers 
(secondary  reactions) . 

The  latter  class  is  by  far  the  larger.  It  can  again  be  sub- 
divided into  two  groups,  the  cathodic  and  the  anodic  depo- 
larizers. It  is  very  seldom  that  a  body  acts  simultaneously 
as  a  cathodic  and  anodic  depolarizer.  More  often  a  cathodic 
(or  anodic)  depolarizer,  by  reacting  with  the  cations  (or  anions), 
acquires  the  faculty  of  now  depolarizing  anodically  (or  cathod- 
ically).  Thus,  for  example,  an  easily  reducible  body  may  be 
changed  by  cathodic  reduction  into  one  easily  oxidized,  i.e. 
accessible  to  the  action  of  the  anions.  However,  it  is  more 
conducive  to  clearness  to  adhere  to  the  division  into-  cathodic 
and  anodic  depolarizers  and  to  determine  the  nature  of  the 
possible  reactions. 

Cathodic  Depolarizers. — Hydrogen  and  metal  ions  pass  to 
the  cathode — if  we  take  no  account  of  the  small  and  unimpor- 
tant number  of  organic  cations.  Hydrogen  and  metals  can 
withdraw  oxygen,  i.e.  deoxidize;  and  the  hydrogen  can  also 
be  added  directly  to  the  compound.  Such  bodies  that  can 
yield  oxygen  or  take  up  hydrogen,  or  do  both  simultaneously, 
are  called  reducible  compounds.  They  themselves  are  hence 
oxidizers  whose  characteristic  property  it  is  to  destroy  positive 
discharges.  The  reaction  at  the  cathode  is  called  reduction. 
Every  cathodic  depolarizer  is  reduced  by  the  electrolysis. 


8  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  reduction  of  nitrobenzene  to  nitrosobenzene  furnishes 
an  example  of  deoxidation : 

C6H5N02 + 2H  -  CGH5NO  +  H20. 

In  the  conversion  of  azobenzene  to  hydrozobenzene  an  addition 
of  hydrogen  takes  place: 

C6H5N  =  NC6H5 + 2H  =  C6H5NH  -  NHC6H5. 

A  withdrawal  of  oxygen  and  addition  of  hydrogen  occurs  simul- 
taneously in  the  reduction  of  nitrobenzene  to  phenylhydroxyl- 
amine : 

C6H5N02 + 4H  =  CsHsNHOH  +  H20. 

Anodic  Depolarizers. — The  conditions  are  somewhat  more 
complicated  at  the  anode.  All  the  anodic  depolarizers  are 
oxidizable,  it  is  true,  even  reducing  substances  which  destroy  the 
negative  charges.  But  the  reaction-picture  is  more  varied  at 
the  anode  than  at  the  cathode — due  to  the  individual  variety 
of  the  anions.  If  the  action  consists  merely  in  a  withdrawal  of 
hydrogen  and  an  addition  of  oxygen,  or  both,  it  is  called  oxi- 
dation. 

Examples  of  such  oxidations  are  the  conversion  of  hydrazo- 
benzene  into  azobenzene : 

C6H5NH  -  NH  -  C6H5  +  0  =  C6H5N  =  NC6H5  +  H20, 

the  conversion  of  benzene  into  hydroquinone  by  a  direct  addi- 
tion of  oxygen : 

C6H6  +  20  =  C6H4(OH)2, 

the  production  of  nitrobenzoic  acid  from  nitrotoluene  by  the 
addition  of  oxygen  and  withdrawal  of  hydrogen: 

N02C6H4CH3  +  30  =  N02C6H4COOH  +  H20. 


THEORETICS.  9 

Discharged  ions,  like  the  halogens,  are  also  often  added  directly 
to  an  organic,  unsaturated  body.  An  addition  occurs,  com- 
parable with  the  addition  of  hydrogen  at  the  cathode, 

CH  CHBr2 

|||+4Br=| 

CH  CHBr2 

or,  a  substitution  takes  place,  i.e.  an  anion — simple  or  compound 
—replaces  an  element  or  group  of  elements  of  the  depolarizer,— 
e.g.  in  the  electrolysis  of  acetone  in  hydrochloric  acid: 

CH3COCH3  +  2  Cl  =  CH2C1COCH3  +  HC1. 

Possibly  the  anion  itself  undergoes  changes  before  it  acts 
upon  the  depolarizer,  so  that  the  organic  compound  can  no 
longer  be  spoken  of  as  a  true  depolarizer  for  the  anion  but 
only  for  its  decomposition  products.  Thus,  in  the  presence 
of  a  base,  the  anion  CH3COO  would  behave  in  such  a  manner 
that,  after  it  was  split  up  into  ethane  and  carbonic  acid,  only 
the  latter  would  react  with  the  base.  However,  such  a  reaction 
can  no  longer  be  regarded  as  an  electrochemical  one. 

It  seems  particularly  difficult  to  determine  in  a  simple 
way  the  nature  of  an  electrolytic  reaction  where  there  are- 
so  many  possible  ways  for  a  reaction  to  take  place.  We  shall 
see  later  on,  however,  that,  by  a  proper  consideration  of  the  sub- 
ject, a  definition  is  obtained. 

Another  form  of  reaction  occurs  in  the  electrolysis  of  organic 
compounds.     While  it  cannot  be  regarded  a.s  purely  electrical, . 
no  more  so  than  the  preceding  one,  it  appears  only  in  a  utilizable 
way  among  the  peculiarities  of  the  electrical  method.     The 
product  resulting  primarily,  or  secondarily,  can  occur  first  in; 
an  unstable  modification,  and  can  then  rapidly  undergo  further 
changes.     I  shall  here  only  refer  to  the  intermediate  formation 
of  phenylhydroxylamine  in  the  reduction  of  nitrobenzene  in 
concentrated   sulphuric    acid,  which,  as   is   well   known,    im- 
mediately rearranges  itself  into  amidophenol: 

C6H5NHOH-»C6H4OHNH2. 


10  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Gattermann  l  has  shown  that  the  unstable  modification  can  be 
isolated  by  adding  benzaldehyde  to  the  original  electrolytic 
fluid.  The  aldehyde  reacts  more  rapidly  with  the  intermediate 
product  phenylhydroxylamine  than  the  sulphuric  acid  can  act 
to  effect  a  molecular  rearrangement. 

Intermediate  phases  of  electrical  oxidation  and  reduction 
can  similarly  be  isolated  by  adding  to  the  electrolytes  various 
substances  which  react  more  rapidly  with  the  phase  than  the 
oxidation  or  reduction  (regulable  by  the  current  conditions) 
can  take  place.  This  artifice,  utilized  by  Lob 2  and  Haber,3 
makes  it  possible  to  obtain  theoretically  important  insights  into 
the  successive  and  often  very  transitory  conditions  of  compli- 
cated processes. 

2.  PROPERTIES  OF  ELECTROLYTIC  PROCESSES. 

The  electrolytic  method  possesses  a  number  of  proper- 
ties which  markedly  distinguish  it  from  all  other  chemical 
methods.  In  the  first  place  the  current  produces  the  effect 
which  the  chemical  method  can  accomplish  only  through  the 
agency  of  certain  materials,  such  as  lead  peroxide,  chromic 
acid,  etc.,  in  the  case  of  oxidations,  and  zinc,  stannous  chloride, 
iron,  etc.,  in  the  presence  of  acids  or  alkalies  in  reductions. 
This  effect  is  solely  produced  by  ion-discharges,  forces  which  are 
ultimately  derived  from  a  source  of  electrical  energy,  i.e.  water 
power  or  coal. 

A  consumption  of  energy  replaces  a  consumption  of  material. 
The  economic  ratio  of  these,  which  is  of  great  practical  impor- 
tance, depends  upon  the  factors  controlling  the  prices  of  material 
and  energy. 

In  such  processes  which  require,  even  in  electrolysis,  the 
presence  of  certain  substances  endowed  with  characteristic 
oxidizing  and  reducing  properties  as  a  necessary  component  in 
the  reaction,  the  actual  material  consumption  is  nevertheless 
very  inconsiderable.  The  substances  in  question,  for  instance 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  3040  (1896). 

2  Ztschr.  f.  Elektrochemie  4,  428  (1898). 

3  Ibid.,  506  (1898). 


THEORETICS.  II 

the  metallic  salts,  need  only  be  present  in  the  electrolyte  in 
very  trifling  quantity,  since,  after  accomplishing  their  purpose 
they  are  regenerated  by  the  current  and  can  be  reused  for 
accomplishing  innumerable  reactions.  In  this  case,  also,  only 
the  question  of  energy  need  be  considered. 

Moreover,  the  electrochemical  method  allows  the  confining 
of  the  reaction  to  a  certain  space  within  the  chemical  system. 
The  reaction  occurs  only  in  the  immediate  neighborhood  of 
the  electrode, — thus  the  reactions  of  the  ions  themselves  take 
place  on  the  electrode  surface  at  the  instant  of  their  discharge, 
those  of  the  depolarizers  in  proportion  to  the  quantity  coming 
in  contact  with  the  electrode  surface,  either  by  diffusion  or 
stirring.  The  extent  of  the  space  in  which  the  reaction  occurs 
therefore  depends  upon  the  extent  of  the  electrode  surface; 
it  can  be  considered  as  an  extremely  thin  layer  which  is  in 
intimate  contact  with  the  electrode.  In  this  layer  the  reaction 
processes  occur  in  accordance  with  the  known  laws  of  reaction 
kinetics,  i.e.  their  velocity  depends  upon  the  concentration  of 
the  active  molecules.  These  are,  however,  the  ions  just  dis- 
charged, either  alone,  when  they  react  with  one  another,  or 
simultaneously  with  the  molecules  of  the  depolarizer.  The 
concentration  of  the  latter  is  independent  of  the  electrical 
conditions,  but  the  concentration  of  the  ions  is  determined  by 
the  intensity  of  the  current,  according  to  Faraday's  law. 

3.  SIGNIFICANCE  OF  THE  VELOCITY  OF  REACTION. 

The  electrically  feasible  reaction  conditions  are  (1)  the 
extent  of  the  reaction  space  and  (2)  the  quantity  of  reactive 
ions  in  the  latter,  i.e.  the  concentration  of  the  ions  can  be 
regulated  in  a  purely  electrical  way  and  within  the  broadest 
limits.  The  highest  dilutions  can  be  realized  just  as  well  with 
weak  currents  and  large  electrode  surfaces  as  the  highest  con- 
centrations with  strong  currents  and  small  surfaces.  That 
most  important  factor  of  reaction  kinetics,  the  reaction  velocity, 
is  thus  determinatively  influenced  by  these  concentrations. 
The  importance  of  the  reaction  velocity  is  especially  fundamen- 


12  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

tal  for  the  course  of  the  reaction;  for  in  the  majority  of  cases 
it  is  a  case  of  processes  vying  with  one  another,  the  reaction 
velocities  of  which  determine  the  preponderance,  and  hence 
the  result,  of  the  one  or  the  other  process. 

The  last  remark,  that  competitive  reactions  occur  almost 
always,  needs  a  brief  explanation.  One  reaction  possibility 
is  electrolytically  always  present — the  liberation  of  the  ions 
in  a  molecular  state  on  the  electrode.  This  liberation  is-  a 
reaction  which  must  not  be  confounded  with  the  discharge 
which  precedes  it.  The  discharge  takes  place  in  accordance 
with  Faraday's  law,  and  since  the  discharged  ions — they  are 
either  atoms  or  "  unsaturated  "  groups  formed  by  dissociation — 
cannot  exist,  they  react  with  a  certain  but  unknown  velocity. 
They  thus  combine  to  form  molecules  or  complexes,  and  the 
stable  end-products  are  liberated  in  conformity  with  Faraday's 
law,  the  quantity  separated  being  proportional  to  the  discharge. 
But  if  a  depolarizer  is  present,  the  discharged  ions  have  the 
opportunity  to  react  with  it  instead  of  being  set  free.  The 
depolarization  reaction  also  takes  place  with  a  certain  velocity. 
The  two  velocities,  however,  are  decisive  for  the  partitive 
ratio  between  an  ionic  liberation  and  a  reaction  with  the  depo- 
larizer. Herein  lies  the  importance  of  reaction  velocities  in 
electrolytic  processes. 

The  question  follows:  How  can  we  regulate  ad  libitum  these 
velocities,  i.e.  usually  make  the  reaction  with  the  depolarizer 
the  most  predominating  one?  Apparently  this  is  only  possible 
ivithin  the  bounds  set  by  the  chemical  nature  of  the  active 
molecules — by  a  shifting  of  concentrations  in  the  reaction 
space,  which  can  be  regulated  on  the  one  hand  by  the  variation 
in  the  quantity  of  the  depolarizer,  and  on  the  other  hand  by 
the  concentration  of  the  discharged  ions  and  the  size  of  the 
reaction  space,  i.e.  the  electrode  surface.  The  velocity  of 
liberation  is  also  increased  by  increasing  the  current  strength, 
upon  which  the  prevailing  concentration  of  the  discharged 
ions  in  the  unit  of  time  depends,  likewise  by  decreasing  the 
electrode  surface,  which  has  the  same  effect  as  the  increase 
in  concentration.  It  will  therefore  be  the  experimental  problem 


THEORETICS.  13 

to  choose  the  current  strength,  electrode  dimension,  and  depo- 
larizer quantity  in  such  a  manner  as  to  produce  the  desired 
effect. 

The  ratio  of  the  current  strength  to  the  electrode  surface  is 
called  current  density.  This  latter  and  the  quantity  of  the 
depolarizer  therefore  are  decisive  factors  in  electrolysis. 

4.  REACTION  VELOCITY  AND  SPECIFIC  EFFECT  OF 
REDUCING  AND  OXIDIZING  AGENTS. 

These  conditions  can  only  give  an  insight  into  the  quanti- 
tative course  of  an  electrolysis.  The  qualitative  course  of  the 
reaction  is  conditioned  by  the  chemical  forces  of  affinity  specific 
of  the  single  elements  or  compounds  and  characteristic  of  the 
reacting  masses. 

In  the  majority  of  the  electrolyses  of  organic  bodies  the 
circumstances  are  very  much  simplified  by  the  fact  that  it 
is  only  a  question  of  two  different  forms  of  reaction,  viz.  reduc- 
tion and  oxidation.  The  limits  within  which  a  reduction  can 
take  place  at  all  are  already  given  in  the  case  of  a  cathodic 
depolarizer  by  its  nature,  no  matter  which  reducing  agent 
is  employed.  For  instance,  only  nitrosobenzene,  phenylhy- 
droxylamine  and  aniline  need  be  considered  in  the  reduction 
of  nitrobenzene,  and  the  chemical  nature  of  the  reducing  ions 
cannot  enlarge  these  boundaries.  Since  the  single  reduction 
phases  are  quantitatively  related  to  one  another,  the  one  follow- 
ing being  always  the  direct  reduction  product  of  the  preceding 
one,  and  since  the  obtainable  phase  depends  solely  upon  the 
more  or  less  strong  reduction,  the  special  efficacy  of  the  various 
reducing  agents  presents  itself  as  a  quantitative  order  which 
can  be  repeated  at  will.  The  individual  properties  of  the 
reducing  agencies  become  mutually  comparable  in  a  quantitative 
way.  For  instance,  if  nitrobenzene  is  reduced  to  aniline  with 
copper  and  sodium  hydrate,  but,  using  zinc  and  sodium  hydrate 
solution,  only  to  azobenzene,  the  specific  action  of  the  copper 
and  zinc  is  shown  qualitatively,  but  the  quantitative  connection 
exists  also  at  the  same  time  that  copper  is  a  stronger  reducing 
agent  than  zinc,  i.e.  a  qualitatively  equal  agent. 


14  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  effects  producible  by  choosing  a  suitable  reducing 
agent  can  also  be  obtained  electrically.  The  important  prob- 
lem arising  in  electrolysis  is  to  convert  the  qualitative  phenom- 
,  ena  into  quantitative  ones,  and  to  find  a  uniform  measure  for 
the  changing  effects.  Naturally,  the  above  applies  in  like 
manner  to  an  oxidizing  agent. 

As  we  have  already  seen,  the  current  density  is  the  regu- 
lator of  the  electrically  obtainable  concentration  conditions 
for  the  discharged  ions,  and  thereby  becomes  codeterminative 
of  the  velocity  of  reaction.  ,  The  obtainable  phase  of  an  oxi- 
dation or  reduction  is  intimately  related  to  the  velocity  of 
reaction,  for  as  soon  as  the  reaction  velocity  of  the  liberation 
of  reducing  or  oxidizing  ions  greatly  exceeds  the  reduction 
or  oxidation  velocity  with  the  depolarizer,  the  reduction  or 
oxidation  stops.  Thus  the  obtainable  phase,  i.e.  the  quality 
of  the  reaction,  occurs  also  as  a  function  of  the  reaction 
velocity. 

5.  ELECTRODE  POTENTIAL  AND  REACTION  MECHANISM. 

The  question  touched  upon  above  can  be  more  fully  defined 
as  follows:  Do  we  know  of  a  factor  which  includes  both  the 
•  concentration  conditions  at  the  electrodes — the  functions  of  the 
current  density  and  depolarizer  concentration — and  also  takes 
into  consideration  the  individual  character  of  the  active  masses,1 
i.e.  the  ions  of  the  depolarizer?  The  answer  is  affirmative. 
All  these  influences  are  contained  in  the  electrode  potential. 

This  claim  becomes  intelligible  if  we  consider  more  care- 
fully the  nature  of  the  electrode  material.  It  is  necessary  to 
choose  a  certain  theory  among  the  various  ones  which  have 
been  proposed — with  more  or  less  justification — on  the  electrical 
mechanism  of  reaction.  I  select  that  one  which  seems  to  me 
to  have  the  best  foundation.  The  fundamental  idea  of  this 
theory  has  been  derived  from  Tafel.2  Its  general  usefulness 

-  1  The  nature  and  the  efficacy  of  the  electrode  metal  are  included  in  the 
term  of  "active  masses",  the  ions.     This  will  be  shown  below. 
2  Ztschr.  f.  phys.  Chemie  34,  199  (1900). 


THEORETICS.  15 

I1  have  explained  in  conjunction  with  R.  W.  Moore.  The 
whole  idea  will  be  here  predicated  and  developed. 

Without  laying  too  much  stress  upon  the  most  modern 
view,  that  of  regarding  electricity  at ormcally  by  means  of  the 
idea  of  electrons,,  all  known  phenomena  justify  us  in  dealing 
with  positive  and  negative  electrical  quantities  as  with  chemic- 
ally active  masses,  and  applying  to  them  the  principles  of  reac- 
tion kinetics. 

The  ions  are  accordingly  chemical  compounds,  so  to  speak, 
of  atoms  and  electrons. 

The  process  in  an  electrolysis  is  the  following:  The  ions 
migrate  to  the  electrodes,  the  cations  to  the  cathode  and  the 
anions  to  the  anode.  This  takes  place  as  soon  as  they  come 
within  such  proximity  of  the  electrodes  that  a  neutralization 
of  the  electricity  can  occur.  We  are  justified  in  assuming  that 
this  phenomenon  takes  place  on  the  border  line  between  the 
metal  and  the  solution  in  such  a  manner  that  the  ions  touch  the 
electrode,  strike  against  it,  but  without  being  on  the  electrode; 
the  discharge  of  the  ions  will  occur  in  an  extremely  thin  layer 
immediately  above  the  surface  of  the  electrode.  In  the  case 
of  elementary  ions,  this  discharging  process  yields  free  ele- 
mentary atoms  of  great  affinity;  complex  ions  give  very  react- 
ive groups  which  are  unsaturated  and  possess  "free  "  val- 
ences, and  hence  are  very  prone  to  react  further. 

The  supposition  of  such  a  discharge  which  precedes,  the 
deposition  is  not  arbitrary,  but  necessary.  The  supposition 
that  the  discharge  does  not  take  place  on  the  electrodes  but  at 
the  latter,  seems  at  first  somewhat  arbitrary.  However,  the 
behavior  of  attackable  cathodes  proves  conclusively  that 
the  discharge  cannot  occur  on  the  electrode.  We  also  arrive 
at  formula  which  conform  to  the  observations,  if  we  suppose 
that  the  discharged  but  not  yet  liberated  ions  obey  the  laws 
of  osmotic  pressure,  i.e.  the  laws  governing  gases.  This  fact 
seems  clear,  and  agrees  with  our  knowledge  of  the  matter, 
if  the  discharged  ions  are  in  a  liquid  layer,  no  matter  how  thin 

1  Ztschr.  f.  phys.  Chemie  47,  418  (1904). 


16  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

this  may  be.  It  is  very  difficult  to  understand,  -  if  the  ions 
discharge  themselves  upon  the  metal  surface.  We  would 
then  be  compelled  to  assume  that  the  solution  of  any  atoms 
in  solid  metals  obeyed  the  laws  of  gases,  an  assumption  which 
is  very  improbable  and  leads,  especially  in  anodic  phenomena, 
to  impossible  consequences. 

The  gist  of  this  view  is  the  strict  division  of  the  electrode 
process  into  the  ionic  discharge,  by  which  the  ions  are  trans- 
ferred into  the  atomistic  or  unsaturated  (very  reactable)  state, 
and  into  the  molecular  separation  of  the  discharged  ions.  This 
second  -process  takes  place  with  a  certain  velocity  the  true 
value  of  which  is  unknown  to  us.  It  is  in  general  so  rapid  that 
discharge  and  separation  appear  to  us  to  occur  simultaneously. 
The  discharge  takes  place  according  to  Faraday's  law;  likewise 
the  separation,  after  a  stationary  equilibrium  prevails  between 
the  discharged  ions,  the  atoms  or  unsaturated  groups,  and 
the  separation  products. 

We  can  write  the  first  process  as  a  cathodic  reaction: 


the  second  as 


whereby  the  second  equation  may  be  perhaps  reversible,  as 
above  mentioned.  Accordingly,  apparent  divergences  from 
Faraday's  laws  may  occur  at  the  beginning  of  the  electrolysis. 

If  we  also  assume  the  first  equation  as  reversible,  the  partici- 
pation of  the  electrolytic  osmotic  pressure  would  follow  from 
simple  reaction-kinetic  considerations. 

The  second  equation  is  of  more  interest  here.  It  takes 
place  evidently  with  a  finite  velocity  so  that  other  velocities 
can  compete  with  it.  This  last  is  afforded  by  the  reaction  of 
the  discharged  ions  with  the  depolarizer.  When  this  velocity 
is  far  the  most  important  one  a  separation  of  ions  cannot  be 
observed,  as  is  the  case  with  many  oxidations  and  reductions. 

Chemical  work,  with  which  a  certain  amount  of  heat  and 
external  work  (increase  in  volume,  overcoming  pressure)  is 


THEORETICS.  17 

often  associated,  is  done  at  the  electrodes.  The  total  work 
in  electrolysis  is  supplied  from  the  electric  energy,  i.e.  from 
the  product  of  potential  and  the  quantity  of  electricity. 
The  quantity  of  electricity  necessary  for  the  discharge  of  a 
gram-equivalent  of  ions  is  always  the  same,  a  conclusion 
drawn  from  Faraday's  laws.  Therefore  the  total  work  accom- 
plished by  a  gram-equivalent  of  ions,  i.e.  the  sum  of  chemical 
work,  external  work  and  possibly  liberated  heat,  must  be  pro- 
portional to  the  electrode  potential.  If  the  electrode  process 
consists  only  of  a  chemical  reaction,  in  a  change  of  the  internal 
energy  of  the  reacting  system,  the  potential-  must  consequently 
be  determinative  for  the  value  of  the  work  of  this  change. 
It  is,  of  course,  an  entirely  different  question  as  to  what 
chemical  products  are  formed.  The  chemically  individual 
character  of  the  reacting  bodies  comes  into  play  here,  the 
known  fact  that  the  end-product  of  a  reaction  —  independent 
of  the  value  of  the  energy  change  taking  place  —  is  chemically 
always  more  or  less  related  to  the  materials  started  out  with. 
The  sequence  of  these  considerations  is  that  equal  potentials 
can  produce  only  like  dynamic  effects. 

If  the  potential  is  expressed  by  the  Nernst  formula, 


in  which  ci  is  the  concentration  of  the  discharged  ions  which, 
obeying  the  laws  of  gases,  seek  to  re-enter  the  electrolyte  with 
a  certain  pressure  —  the  electrolytic  osmotic  pressure  —  and  c2 
is  the  concentration  of  the  ions  in  the  electrolyte,  it  is  very 
evident  that  the  potential  must  contain,  apart  from  the  ionic 
concentration  of  the  electrolyte,  all  influences  which  determine 
the  concentration  of  the  discharged  ions  (ci).  These  influences 
are,  primarily,  the  current  density  whose  size  regulates  the 
number  of  the  ions  discharged  in  a  unit  of  time  at  a  given 
electrode  surface,  hence  regulating  its  concentration;  second- 
arily, the  reactions  of  the  ions  with  one  another  and  with  the 
depolarizer.  For  variations  in  the  concentration  of  the  value 


18  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Ci  occur  through  both  processes  and,  since  the  velocity  of  the 
reaction"  of  the  discharged  ions  with  the  depolarizer  also  de- 
pends upon  its  chemical  nature  and  concentration,  these  two 
last-mentioned  factors  are  also  embraced  by  the  potential. 

A  more  thorough  knowledge  of  these  relations  is  gained  by  a 
consideration  of  the  typical  electrode  processes. 

6.  ELECTRODE  PROCESSES. 
A.  Cathodic  Processes. 

a.  Unattackable  and  Attackable  Cathodes. 

In  organic  chemistry  only  those  cathode  processes  are  of 
importance  which  occur  with  the  reduction  of  an  organic 
depolarizer.  This  reduction  is  done  by  the  ions  discharged  at 
the  cathode.  The  chemical  nature  of  these  ions  can  be  very 
variable  and,  conjointly  therewith,  the  reduction  can  occur  in 
a  variable  manner. 

In  acid  solution — assuming  the  depolarizer  to  be  a  non- 
electrolyte — hydrogen  ions  will  occur,  and  in  alkaline  solutions 
alkali  ions,  and  by  making  suitable  additions  any  desired  kind 
of  ions  can  be  brought  into  action  at  the  cathode;  thus  any 
metal  ions  may  be  set  free.  The  metal  ions  are  either  added 
directly  to  the  electrolyte  in  the  form  of  a  metallic  salt  or 
hydroxide,  or  they  are  derived  from  the  cathode  metal  itself, 
in  case  the  cathode  is  ' '  attackable  ",  and  pass  from  this  into 
the  electrolyte. 

The  various  reduction  processes  can  be  brought  about  simply 
if  the  cathode  metal  is  primarily  considered  and  a  distinc- 
tion is  made  between  attackable  and  unattackable  cathodes. 
The  former  are  such  as  give  no  active  ions  in  the  presence  of 
the  respective  electrolyte  and  depolarizer,  so  that  only  the 
cations  of  the  electrolyte  can  be  shown  to  be  discharged  by  the 
current.  Attackable  cathodes  are  those  which  send  traceable 
quantities  of  ions  into  the  electrolyte  during  the  passage  of  the 
current,  or  in  its  absence.  Naturally,  only  those  attackable 
cathodes  which  can  yield  reducing  ions  are  of  interest  here. 

Since  some  investigators  seen  to  believe  that  every  reduc- 


THEORETICS.  19 

tion  must  be  referred  to  the  action  of  hydrogen,  let  it  be  emphat- 
ically pointed  out  here  that,  besides  many  chemical  phenomena, 
the  fact  that  it  is  immaterial  whether  the  reduction  is  made 
at  an  attackable  cathode  or  by  the  addition  of  the  ions  of  this 
cathode  metal  to  the  electrolyte  at  an  unattackable  electrode 
proves  the  reducing  capacity  of  the  metal.  In  both  cases 
similar  results  are  obtained.  But  if  ions  of  attackable 'metals 
are  added,  this  metal  is  not  deposited  on  an  unattackable 
electrode  so  long  as  sufficient  quantities  of  the  depolarizer  are 
present  and  the  velocity  of  depolarization  sufficiently  outweighs 
the  velocity  of  discharge.  Although  the  cathode  metal,  say 
platinum,  always  remains  the  same,  an  effect  occurs  neverthe- 
less, similar  to  that  which  would  be  obtained  at  a  cathode 
composed  of  the  attackable  metal  in  the  electrolyte.  The 
conclusion  follows  necessarily  that  these  metal  ions  in  the 
electrolyte,  and  not  the  hydrogen  atoms,  determine  the  reducing 
action  by  their  separation  on  or  in  the  electrode. 

We  can  hence  consider  conjointly  the  case  of  attackable 
electrodes  with  that  of  the  presence  of  metal  ions  in  the 
electrolyte  at  unattackable  electrodes,  and  contrast  this  with  the 
reduction  by  hydrogen  at  unattackable  electrodes. 

For  the  latter  we  will  suppose  that  the  hydrogen  atoms 
discharge  themselves  in  the  cathode  boundary  surface,  and 
that  these  discharged  ions  have  two  reaction  possibilities  at  their 
disposal.  They  are  either  separated  molecularly  on  the  cathode, 
or  they  reduce  the  depolarizer.  The  reduction  velocities  of  both 
processes  are  determinative  for  the  ratio  of  division.  If  the 
reduction  takes  place  far  more  quickly  than  the  formation 
of  hydrogen  molecules,  practically  no  hydrogen  will  be  evolved. 
The  velocity  of  hydrogen  formation  is  hence  of  importance  in 
the  utilization  of  the  current  action  for  reduction.  It  depends 
to  a  great  degree  upon  the  chemical  nature  and  surface  condi- 
tion of  the  cathode,  and  is  very  likely  related  to  the  catalytic 
nature  of  the  metal.  These  phenomena  will  be  considered 
conjointly  under  the  discussion  on  "  excess  potential/' 

Ions  are  sent  off  from  attackable  cathodes  immediately  into 
the  electrolyte,  so  that  the  relations  in  the  latter  are  qualita- 


20  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

tively  the  same  as  when  metal  ions  are  added  directly  to  the 
electrolyte.  The  metal  employed  as  cathode  is  hence  immaterial 
for  the  effect  so  far  as  it  has  not  actually  reacted  with  the  elec- 
trolyte, and  can  often  be  replaced  by  an  unattackable  cathode. 

Under  these  conditions  the  metal  ions  play  the  role  of 
hydrogen  atoms,  as  above  explained.  They  discharge  them- 
selves in  the  cathode  boundary  surface  and,  depending  upon 
their  reaction  velocities,  affect  the  reduction  of  the  depolarizer 
and  the  metallic  deposition.  With  a  great  reduction  velocity, 
therefore,  no  metal  whatever  is  deposited  on  the  cathode  so  long 
as  sufficient  quantities  of  the  depolarizer  are  present.1 

An  important  result  of  these  considerations,  and  one  which 
confirms  the  observations,  is  the  knowledge  obtained  that  all  ions, 
which  reduce  when  discharged,  are  again  converted  by  this  reduction 
performance  into  the  ionic  state  and  are  not  at  all  separated. 

b.  Excess  Potential  and  the  Reduction  Action. 

Although  the  evolution  of  hydrogen  by  galvanic  action  at 
platinized  platinum  electrodes  is  a  well-nigh  reversible  phenom- 
enon, it  proves  irreversible  at  all  other  cathodes. 

To  convert,  in  a  given  electrolyte,  a  gram-equivalent  of 
hydrogen  from  the  ionic  into  the  molecular  state  at  atmospheric 
pressure,  the  same  amount  of  work,  which  is,  of  course,  depen- 
dent upon  the  beginning  and  end  condition,  is  always  required. 
But  the  electrical  work  is  different  at  different  electrodes  and, 
since  the  same  quantity  of  electricity  is  combined  with  a  gram- 
equivalent  of  hydrogen,  trie  potential  of  hydrogen  evolution  is 
different  with  the  individual  metals.  Naturally,  with  the 
equality  of  the  initial  and  final  state  the  surplus  of  the  electrical 
work  performed  must  be  compensated  by  an  equivalent  gain 
in  work.  Calorific  phenomena  probably  accompany  the  in- 
crease in  required  work  necessary  for  the  hydrogen  evolution; 
the  results  of  experimental  work  on  this  subject,  however,  are 
not  yet  at  our  disposal.  Excess  potential  is  the  excess  of  the 
discharge  potential  of  hydrogen  over  the  potential  value  of  a 

1D.  R.  P.  117007  (1900)  of  C.  F.  Boehringer  u.  Sohne;  Lob  and  Moore, 
Ztschr.  f.  phys.  Chemie  47,  418  (1904). 


THEORETICS  21 

hydrogen  electrode  in  the  corresponding  electrolyte.  The 
quantity  of  heat  produced  by  the  excess  potential  can  be  very 
considerable.  If  we  designate  the  absolute  potential  of  the 
reversible  hydrogen  evolution  by  a,  and  the  value  of  the  excess 
potential  by  e,  then  the  electrical  work  in  the  separation  of  a 
gram-equivalent  of  gaseous  hydrogen  in  the  first  case  is 

A=96540a; 
and  in  the  second 

Ai=96540(a+e). 

Since  the  total  work  in  both  cases  must  be  equal,  there  results, 
if,  as  assumed,  a  production  of  a  quantity  of  heat  q  occurs,  the 
equation 


or 


For  mercury  e  is  =  0.78  volt,  from  which  <?=  18026  cal.  results. 
[96540  coul.  X  1  volt  =  23110  cal.] 

According    to    Caspari,1  these    excess  potentials  have  the 
following  values  with  individual  metals: 

At  platinized  platinum  .............  0.005  volt. 

"  bright  platinum  .................  0.09  " 

"  nickel  ..........................  0.21  " 

"  copper  .........................  0.23  " 

11  tin  ............................  0.53  "' 

"  lead  ...........................  0.64  " 

"  zinc  ...........................  0.70  " 

'  '  mercury  .......................  0  .  78 


cc 


Nernst,  who  introduced  the  conception  of  excess  potential  into 
the  science  of  electrochemistry,  accepts  as  the  cause  of  these 
phenomena  the  varying  solubility  of  hydrogen  in  the  metals. 

1  Ztschr.  f.  phys.  Chem.  30,  89  (1899). 


22  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Since  the  energy  of  reduction  depends  chiefly  upon  the  height 
of  the  cathode  potential,  the  higher  the  excess  potential  is  the 
stronger  the  former  must  be,  so  long  as  hydrogen  is  the  reduc- 
ing agent. 

A  great  number  of  facts  agree  1  with  this  conception.  The 
assumptions  regarding  the  electrical  reduction  mechanism, 
according  to  which  the  discharge  of  hydrogen  ions  must  be 
distinctly  distinguished  from  their  molecular  separation,  lead 
to  the  same  conclusions.  The  reaction  velocity  of  molecular 
formation  from  the  discharged  hydrogen  ions  is  lowered  at 
metals  with  excess  potential,  so  that  the  division  between 
molecular  formation  and  reduction  of  the  polarizer  turns  in 
favor  of  the  latter.  This  retardation  of  hydrogen  evolution 
is  shown  in  the  higher  potential,  in  the  excess  voltage.  With 
a  high  excess  voltage  in  the  discharging  space  stronger  con- 
centrations of  discharged  reactive  hydrogen  ions  can  accu- 
mulate, so  that  the  reduction  of  bodies  reducible  with  diffi- 
culty, which  does  not  occur  at  platinized  platinum  electrodes, 
succeeds  at  zinc  or  mercury  cathodes. 

Since  in  the  fundamental  views  a  separation  of  hydrogen 
in  or  upon  the  cathode  does  not  enter  into  the  question,  the 
close  connection  of  this  separation  with  the  solubility  of  hydro- 
ogen  in  the  metals  cannot  be  conceived.  In  this  case  it  is 
more  plausible  to  think  of  the  reaction  being  catalytically 
influenced  by  the  metal.  Accordingly,  the  platinized  platinum 
would  be  the  metal  which  would  most  strongly  accelerate  the 

reaction 

2H=H2.2 

The  higher  the  excess  potential  the  smaller  the  catalytic  accel- 
eration of  the  reaction,  and  hence  the  stronger  the  concurrent 
reduction. 

JS.  Tafel,  Ztschr.  f.  phys.  Chem.  34,  227  (1900);  Lob,  Ztschr.  f.  Elektro- 
chemie  7,  320,  333  (1900-1901);  Coehn,  Ztschr.  f.  Elektrochemie  9,  642 
(1903). 

2  E.  Miiller  gives  a  similar  explanation,  but  does  not  mention  the  catalytic 
action,  which  is  here  particularly  emphasized.  Ztschr.  f .  anorg.  Chem.  26, 
1  (1901). 


THEORETICS  23 

The  idea  of  excess  potential  is  useful  in  applying  the  process 
of  separating  a  certain  kind  of  ions  at  unattackable  cathodes. 
For  reduction  it  has  up  to  the  present  only  been  proved  for 
hydrogen;  it  is  nevertheless  possible  that  the  separation  poten- 
tial of  every  ion  changes  with  the  nature  of  the  electrode, 
since  the  opportunity  for  the  reaction  of  discharged  ions  being 
catalytically  influenced  to  form  stable  molecules  is  always 
present.  E.  Miiller  1  and  Coehn  2  have  shown  that  the  excess 
potential  phenomenon  also  occurs  in  anodic  processes. 

The  generally  disseminated  idea,  however,  that  the  excess 
potential  of  hydrogen  also  plays  a  part  in  the  case  of  attackable 
cathodes  is  untenable.  With  metals  which  furnish  reducing 
ions — and  each  cation  is  capable  of  reducing — hydrogen  does 
not  take  part,  or  at  least  plays  only  a  secondary  role.  The 
specific  reducing  actions  of  copper,  zinc,  tin,  and  lead  cathodes 
are  not  to  be  explained  by  the  excess  potential  of  hydrogen. 
Since  attackability  is  also  a  function  of  the  electrolyte,  the 
rule  of  excess  voltage  may  be  applicable  in  one  case  and  not 
in  another.  For  example,  Tafel 3  could  explain  the  strong 
reducing  action  of  a  lead  cathode  in  sulphuric-acid  solution 
by  the  high  excess  potential  of  the  lead,  while  the  same  metal 
is  attackable  in  alkaline  electrolytes  and  yields  reducing  ions, 
whereby  the  hydrogen  action  seems  excluded.4 

c.  Concerning  Substances  Reducible  with  Difficulty. 

Besides  the  discussion  on  the  strong  depolarizers  thus  far 
considered,  it  will  be  well  to  make  a  few  special  remarks  on 
substances  reducible  with  difficulty.  The  insight  into  the  theo- 
retical relations  here  existing  has  not  yet  been  cleared  up,  and 
is  much  more  difficult  than  in  the  case  of  the  substances  which 
consume  practically  all  the  cations  which  are  discharged. 
However,  it  is  not  at  all  necessary  to  add  special  views  to 
those  already  generally  developed.  They  suffice  for  the  present 

1  Jahrb.  f.  Elektrochemie  VIII,  292;   Ztschr.  f.  anorg.  Chem.  26,  1  (1901) 

2  Ztschr.  f.  Elektrochemie  9,  642  (1903). 

3  Ztschr.  f.  phys.  Chemie  34,  199  (1900). 

4  Cf.  Lob  and  Moore,  Ztschr.  f.  phys.  Chem.  46,  427  (1904). 


24  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

in  explaining  the  phenomena  occurring  here,  and  we  may  pos- 
sibly get  along  with  a  uniform  interpretation.  The  deciding 
importance  of  reaction  velocities  on  the  course  of  every  chemi- 
cal action  requires  of  us  a  clear  explanation  of  the  relation 
of  the  influences  cooperating  in  the  course  of  the  reaction  to 
that  fundamental  factor,  the  velocity  of  reaction.  It  will, 
therefore,  be  well  to  consider  these  influences  from  this  par- 
ticular side  and  to  ask  what  relation  do  the  electrical  factors 
bear  to  the  reaction  velocity,  and  in  what  manner  do  they 
act  on  the  latter.  It  appears  that  the  reducing  action  of 
difficultly  reducible  substances  at  unattackable  cathodes  takes 
place  differently,  depending  upon  the  material  of  the  latter. 
This  diversity  can  be  explained  by  unequal  reduction  veloci- 
ties. The  later  depend  upon  the  concentration  of  the  react- 
ing substances  which — so  far  as  the  ions  alone  to  be  taken 
into  consideration  are  concerned — is  regulated  by  the  current 
strength,  the  chemical  resistance  of  the  system,  i.e.  the 
nature  of  the  medium,  and  by  catalytic  influences  which, 
with  the  choice  of  suitable  conditions,  are  to  be  ascribed  to  the 
electrode  metal.  The  measurable  electrical  factor,  the  poten- 
tial, comprises  a  part  of  these  influences,  and  it  is  of  conse- 
quence to  thus  know  the  single  moments  determining  the 
potential  in  such  a  manner  that  the  connection  with  the  reac- 
tion velocity  remains  clear. 

Substances  reducible  with  difficulty  are  such  possessing 
trifling  polarizing  value,  and  whose  addition  to  the  electrolyte 
•  unessentially  lowers 1  the  cathode  potential  which  was  deter- 
mined for  the  pure  electrolyte.  The  relations  existing  here  have 
been  fully  investigated  by  Tafel  and  his  pupils. 

In  the  case  of  substances  of  this  nature,  reduced  in  acid 
solution  at  practically  unattackable  cathodes,  the  consump- 
tion of  hydrogen  by  the  depolarizer  is  never  equal  to  the 
quantity  of  hydrogen  liberated  by  the  current,  so  that  a  division 

1  With  caffeine  and  succinimide,  in  sulphuric-acid  solution,  an  increase  in 
potential  occurs  at  certain  electrodes  (see  below).  (Naumann:  Concerning 
the  Influence  of  the  Cathode  Potential  on  the  Electrolytical  Reduction  of  Sub- 
stances Reducible  with  Difficulty.)  Thesis.  Wiirzburg,  1904. 


THEORETICS.  25 

always  takes  place  into  hydrogen  consumed  by  the  reduction, 
and  hydrogen  evolved  molecularly  as  a  gas.  According  to  the 
preceding  explanations,  it  is  clearly  evident  that  the  excess 
potential  must  play  a  decisive  part  in  all  these  cases,  since  it 
forms  an  expression  for  the  above-mentioned  ratio  of  division 
in  proportion  to  the  reaction  velocities.  If  we  consider  the 
velocity  of  formation  of  molecular  hydrogen  as  a  process 
influenced  catalytically  by  the  electrode  material,  the  value  of 
the  excess  potential  of  the  electrode  in  pure  acid  without  the 
depolarizer  will  be  decisive  for  the  reduction  energy,  provided 
that  the  catalytic  property  is  not  modified  by  the  depolarizer. 
The  latter,  under  similar  experimental  conditions,  and  provided 
no  catalytic  acceleration  of  the  reduction  itself  occurs,  reacts 
always  with  a  similar  velocity  with  the  hydrogen.  Thus  a 
change  in  the  division  ratio  between  hydrogen  evolution  and  re- 
duction is  only  determined  by  a  change  in  velocity  of  the  former. 
Naumann's l  experiments  agree  with  this.  He  showed  that  the 
velocity  with  which  caffeine  is  reduced  at  lead  cathodes  depends 
upon  the  cathode  potential  in  pure  acid.  The  reduction  occurs 
the  more  energetically  the  higher  the  excess  potential  is  in  pure 
acid.  This  rule  does  not  apply  when  the  cathode  metal  materi- 
ally influences  the  actual  velocity  of  reduction,  the  reaction 
between  hydrogen  and  the  depolarizer.  Thus  caffeine  is  reduced 
more  quickly  at  mercury  than  at  lead  electrodes,  although 
both  metals  possess  the  same  cathode  potential,  or  the  same 
excess  potential  in  pure  acid.  The  velocity  of  the  molecular 
evolution  of  hydrogen  can  also  be  retarded  by  the  presence  of 
the  caffeine  molecules,  as  the  caffeine  molecules,  to  use  a  crude 
illustration,  increase  the  chemical  resistance  in  this  reaction  at 
the  electrode  surface.  In  this  case  the  excess  potential  increases, 
and  with  it  the  cathode  potential.  At  the  same  time  the 
depolarizing  action  of  the  caffeine  seeks  to  lower  the  cathode 
potential.  If  the  first  action — with  small  quantities  of  caffeine 
—is  the  stronger,  an  increase  in  potential  is  at  first  observed  in 
spite  of  the  addition  of  caffeine.  By  adding  larger  quantities 

1  See  note  on  page  24. 


^6  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

of  caffeine,  the  potential  is  finally  caused  to  drop  (by  stronger 
depolarizing  effects) .  This  phenomenon  occurs  at  lead  but  not 
at  mercury  cathodes  (Naumann).  In  the  latter  case  only  the 
depolarizing  action  of  caffeine  is  shown;  this  is  perhaps  depen- 
ent  upon  the  different  surface  conditions  of  lead  and  mercury. 

The  cathode  potential  is  determined  on  the  one  hand  by 
the  electrolytic  osmotic  pressure  of  the  cathode,  i.e.,  by  the 
quantity  of  hydrogen  which  is  evolved  electrolytically  at  unat- 
tackable  cathodes  in  the  unit  of  time.  With  this  hydrogen,  the 
ions  discharged  in  the  boundary  layer,  which  unite  to  form 
molecular  hydrogen,  are  in  equilibrium.  This  electrolytic 
osmotic  pressure  is,  therefore,  independent  of  the  quantity  of 
hydrogen  used  by  the  depolarizer.  Moreover,  the  potential  is 
determined  by  the  concentration  of  the  hydrogen  ions  in  the 
electrolyte,  which  concentration  can  be  taken  as  constant 
when  strong  acids  are  used. 

The  conclusions  (likewise  found  by  Naumann)  to  be  drawn 
from  these  considerations1  are  the  following:  At  mercury 
cathodes,  whose  excess  potential  is  not  influenced  by  the 
caffeine,  the  cathode  potential  must  so  adjust  itself  at  every 
moment  during  the  reduction  as  if  only  the  electrolytic  evolu- 
tion of  hydrogen  occurred  and  the  current  consumed  in  the 
reduction  of  the  caffeine  did  not  influence  its  height.  At  lead 
electrodes,  however,  the  cathode  potentials  are  always  some- 
what higher  during  the  reduction  than  in  the  same  electro- 
lytic hydrogen  evolution  in  the  pure  acid,  since  the  increase  in 
.^excess  potential  caused  by  the  caeffeine  is  added  to  it. 

It  is  evident — from  a  consideration  of  these  variously  pos- 
sible influences,  such  as  the  change  in  the  excess  potential 
•  caused  by  the  depolarizer,  the  catalytic  action  of  the  metal 
upon  the  velocity  both  of  the  molecular  formation  of  hydrogen 
and  the  reaction  between  hydrogen  and  the  depolarizer — that 
the  value  of  the  cathode  potential  is  conditioned  by  a  series  of 


1  Naumann,  in  his  dissertation,  gives  another  deduction  which,  however, 
contains  the  hypothesis  that  the  hydrogen  formation  and  the  reduction  reac- 
tions are  of  the  same  order. 


THEORETICS.  27 

moments  which  can  be  independent  of  one  another.  Hence 
the  reduction  effect  can  vary  even  with  equal  potentials  at 
different  electrodes,  which  is  true,  for  example,  with  caffeine; 
at  lead  and  mercury  cathodes.1 

B.  Anodic  Processes. 

A  theoretical  insight  into  this  part  of  the  electrolysis  of 
organic  compounds  is  much  less  clear  than  in  the  case  of  cathodic 
processes. 

The  pure  action  of  oxygen  is  in  every  way  comparable  with' 
that  of  hydrogen.  Only  a  greater  variety  is  here  possible,, 
because  ozone  as  well  as  oxygen  can  be  formed.  At  platinum 
electrodes,  for  instance,  the  formation  of  oxygen  occurs  at  1.08 
volts  as  measured  with  a  hydrogen  electrode  at  zero  value, 
and  that  of  ozone  at  1.67  volts.  Moreover,  the  great  suscepti- 
bility of  the  carbon  compounds  towards  oxygen,  as  already 
alluded  to,  which  may  easily  lead  to  their  complete  destruction,, 
and  the  great  number  of  oxidation  phases  to  which  each  molecule 
may  in  a  greater  or  less  degree  be  subject,  render  difficult  an 
insight  into  the  electrical  oxygen  actions. 

It  has  already  been  mentioned  that  the  excess  potential 
phenomenon  occurs  also  with  the  oxidation  phenomena.  Thus; 
it  is  possible  to  conyert  p-nitrotoluene  into  p-nitrobenzoic  acid 
at  lead-peroxide  anodes,  while  at  platinum  anodes  only  the 
alcohol  is  formed.  It  still  seems  inexplicable  how  this  peculiar 
action  of  the  anode  material  takes  place.  The  simplest  yet 
sufficient  explanation  is  to  assume  .that  the  anode  is  capable  of 
influencing  catalytically  the  oxidation  process  as  well  as  the 
formation  of  molecular  oxygen.  If  the  first  process  is  acceler- 
ated and  the  second  retarded,  we  obtain  the  excess  potential 
by  which  the  evolution  of  oxygen  occurs  only  at  a  higher 
potential.  Inversely,  the  oxygen  and  ozone  formation  can  be 
made  reversible,  and  the  oxidizing  action  decreased. 

A  further  complicating  moment  in  electrolytic  oxidations, 
as  opposed  to  reductions,  is  the  variety  of  possible  ionic  actions. 

1  Tafel  and  Schmitz,  Ztschr.  f.  Elektrochemie  8,  281  (1902). 


128  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

While  the  process  at  the  cathode  always  ends  finally  in  with- 
drawal of  oxygen  or  in  taking  up  of  hydrogen,  the  number  of 
possible  reactions  at  the  anode — aside  from  solution-phenomena, 
which  are  without  interest  here — is  a  much  greater  one.  For, 
each  ion  which  is  capable  of  substituting  can  pass  into  the 
reactive  state  at  the  anode  and  produce  reactions  which 
cannot  be  numbered  with  the  real  oxidations.  In  the  first 
place  numerous  substitutions  can  occur  in  difficultly  oxidizable 
bodies,  especially  aromatic  compounds,  for  instance  the  chlori- 
nation  of  phenols  and  phthaleiins,  nitration  of  acids,  diazotizing 
of  amines,  etc.  Substitution  and  oxidation  processes  often 
occur  simultaneously,  as  in  the  electrolytic  formation  of  iodo- 
form  from  alcohol. 

A  great  many  more  individual  varieties  of  reactions  must 
be  taken  into  consideration  in  anodic  processes.  However, 
the  same  fundamental  law  holds  good  for  each  of  the  separate 
possible  processes  as  with  the  reductions,  in  that  the  energy 
of  the  action  of  the  anion  is  determined  by  the  anode  potential. 
Thus  0.  Dony  Henault,1  carefully  observing  limited  anode 
potentials  in  the  electrical  oxidation  of  the  alcohol,  could 
obtain  acetaldehyde  or  acetic  acid  at  will. 

The  reason  for  the  prominence  of  reduction  processes  as 
apposed  to  the  less  prominent  electrical  oxidations  has  already 
been  given.  Besides  the  complexity  of  the  phenomena,  it 
must  be  taken  into  consideration  that  the  oxygen  evolved  at 
platinum  anodes  has  a  low  potential.  The  action  of  an  oxi- 
dizer  depends  upon  the  oxidation  potential  with  which  the 
oxygen  attacks  the  depolarizer.  Even  though  the  oxidation 
potential  can,  within  certain  limits,  be  varied  by  the  anode 
potential,  for  instance  by  the  material  of  the  anode,  it  never- 
theless does  not  attain  the  value  of  the  strong  chemical  oxi- 
dizers,  as  for  example  chromic  acid  or  permanganic  acid. 
This  follows  from  the  small  activity  of  electrolytic  oxygen  in 
regard  to  separate  bodies. 

Since  it  is  not  possible   always  to  obtain  the  entirely  indi- 

1  Ztschr.  f.  Elektrochemie  6,  533  (1900). 


THEORETICS.  29 

vidual  action  of  these  two  bodies  on  organic  compounds  with 
the  aid  of  electrolytically  evolved  oxygen,  it  seemed  advisable 
to  use  the  chemical  oxidizers,  which  have  already  been  men- 
tioned, in  the  electrolytic  cell.  This  was  done  by  employing 
the  electrical  process  only  for  the  regeneration  of  the  chromic  or 
permanganic  acids  which,  as  such,  oxidize  organic  bodies  in 
a  purely  chemical  way,  being  themselves  converted  thereby 
into  lower  stages  of  oxidation.  The  advantage  of  such  a  method 
lies  in  a  saving  of  both  the  oxidizing  acids,  because,  on  account 
of  the  regeneration  to  their  highest  state  of  oxidation,  very 
small  quantities  suffice  to  oxidize  unlimited  quantities  of  organic 
bodies.  This  oxidation  process  is  hence  both  a  secondary  and 
a  chemical  one.  Nevertheless,  it  possesses  the  essential  feat- 
ures of  an  electrochemical  process,  the  substance  being  replaced 
by  the  energy. 

Attackable  anodes,  which  are  brought  into  solution  by 
the  anions  of  the  electrolyte,  are  of  no  value,  or  only  of  a  wholly 
secondary  one,  in  the  electrolysis  of  organic  compounds.  But 
in  such  cases  where,  by  reason  of  the  attackability,  oxidizing 
substances  are  formed  on  the  anode,  the  latter  can  assume  the 
functions  of  an  oxygen  carrier.  Thus,  if  a  lead  anode  is  super- 
ficially coated  with  lead  peroxide,  this  latter  effects  the  oxida- 
tion, being  in  turn  reduced  but  always  regenerated  by  the 
current.  But  if  a  lead-peroxide  anode,  prepared  in  this  man- 
ner, acts  merely  by  means  of  its  excess  potential  for  the  dis- 
charged oxygen,  without  reacting  directly  with  the  depolarizer, 
it  naturally  exercises  only  the  functions  of  an  unattackable 
anode. 

Finally  may  be  mentioned  the  purely  catalytic  action  of 
the  electrodes  upon  the  reaction  products  produced  by  the 
electrolysis,  a  sphere  of  phenomena  which  lies  outsider  the 
purely  electrical  relations.  This  is  the  case,  for  instance, 
in  the  decomposition  of  hydrogen  peroxide  by  electrical 
oxidation  at  platinum  anodes  into  water  and  oxygen.  But 
€ven  the  electrical  conditions  can  be  modified  by  such  reac- 
tions, if  changes  in  the  concentration  relations  of  the  pre- 
dominating ions  are  combined  with  them. 


30  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

7.  THEORY    OF   THE    REACTION    VELOCITY   IN    ELECTROLYTIC 

PROCESSES. 

The  ease  with  which  the  reaction  conditions  can  be  con- 
trolled makes  electrolytic  processes  especially  adapted  for 
studying  the  laws  of  reaction,  particularly  those  of  reaction 
velocities.  The  dependence  of  the  reacting  agents  upon  the 
current  strength,  according  to  Faraday's  laws,  makes  it  po&- 
sible  to  vary  ad  libitum  the  temporal  total  course  of  a  reaction 
within  wide  limits — a  possibility  which  in  purely  chemical 
operations,  by  changing  the  conditions  of  pressure  and  tempera- 
ture, exists  to  a  far  less  extent. 

Attempts  have  not  been  lacking  to  regard  electrical  proc- 
esses from  a  reaction-kinetic  point  of  view,  and  to  use  them 
directly  for  determining  reaction  velocities.  Even  though 
these  experiments  are  based  naturally  upon  single  simple 
examples  —  mostly  reduction  experiments  —  their  theoretical 
results  have,  especially  for  physicochemical  speculations  of 
organic  reactions,  such  general  importance  that  the  reasoning 
involved  in  the  most  important  theories  will  briefly  be  out- 
lined here. 

a.  The  Diffusion  Theory. 

Since,  according  to  the  preceding  descriptions,  the  reac- 
tion space  of  electrolytic  processes  consists  of  an  extremely 
thin  layer  in  contact  with  the  electrode — the  contact  surface 
of  electrolyte  and  electrode — these  processes  can  generally  be 
regarded  as  reactions  in  heterogeneous  systems.  Nernst 1 
has  proposed  a  theory  for  such  systems,  which  has  been 
tested  experimentally  by  Brunner.2  The  principle  of  this 
theory  consists  in  basing  the  reaction  velocities  on  the  dif- 
fusion velocity. 

The  equilibrium  between  two  phases  at  their  boundary 
surface  must  be  produced  with  extremely  great  rapidity, 

1  Ztschr.  f.  phys.  Chemie  47,  52  (1904).    See  also  the  earlier  investigation: 
Noyes  and  Whitney,  ibid.  23,  689  (1897) 

2  Ztschr.  f.  phys.  Chem.  47,  55  (1904) 


THEORETICS.  31 

otherwise  infinitely  great,  or  at  least  very  great,  forces  would 
develop  between  the  extremely  close  points  between  which 
the  reaction  occurs.  These  would,  however,  bring  about 
the  equilibrium  practically  instantly,  In  such  a  case  the 
reaction  velocity  is  conditioned  by  the  velocity  with  which 
the  mobile  components  reach  the  border-line  of  the  phases, 
i.e.  by  the  diffusion  velocity. 

The  contact  surface  of  both  phases  will  now  actually  pos- 
sess a  thin  but  measurable  layer  of  the  thickness  d,  within  which 
the  whole  diffusion  process  occurs. 

If  we  designate  the  concentration  of  the  diffusing  sub- 
stance at  the  surface  of  the  fixed  phase  by  C,  its  concentra- 
tion in  the  solution  by  c,  its  diffusion  constant  by  D,  and  the 
surface  of  the  solid  body  by  F,  then  in  the  period  dt  the  quan- 
tity of  substance 


will   diffuse   to   the   contact  surface   and  immediately  react. 
The  speed  of  reaction  becomes 


dt 

If  we  consider  that  C  possesses  an  extremely  small  and 
negligible  value,  on  account  of  the  equilibirum  which  occurs 
instantly,  the  following  equation  results: 

dx_DF 

dt~"~T'c' 

The  speed  of  reaction  is  proportional  to  the  concentration 
of  the  diffusing  substance. 

In  applying  these  results  to  electrochemical  reactions  there1 
is  to  be  added  only  the  condition  that  the  concentration  of 
the  reacting  substance  in  the  immediate  vicinity  of  the  elec- 
trode must  always  possess  a  very  small  value,  which  can 
easily  be  attained  by  choosing  a  suitable  current  tension.  Then 
the  reaction  velocity  will  depend  only  upon  the  quantity  of- 


32          ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

the  substance  reaching  the  electrode.  Electrolytic  transfer- 
ence must  be  considered  as  well  as  the  diffusion,  if  ions  are 
involved. 

Since  the  quantity  of  the  discharged  ions  depends  upon 
the  current  strength,  it  represents  a  measure  of  the  reaction 
velocity,  if  (1)  side  reactions  are  excluded  —  for  instance,  if  no 
ions  are  discharged  without  reacting  —  and  (2)  the  current 
strength  chosen  is  not  so  small  that  the  reaction  velocity 
possesses  a  higher  value  than  the  discharging  velocity  of  the  ions 
regulated  by  the  intensity. 

In  other  words:  The  current  strength  is  then  only  a  direct 
measure  of  the  reaction  velocity,  if  the  maximum  current 
strength  at  which  all  the  liberated  ions  are  just  able  to  react 
is  employed.  The  production  of  this  condition  can  be  easily 
recognized  experimentally  by  the  fact  that  the  least  increase 
of  this  maximum  intensity  leads  to  side  reactions,  most  fre- 
quently to  a  molecular  separation  of  the  discharged  ions. 

Before  the  Nernst  theory  was  proposed,  H.  Goldschmidt  1 
had  already  employed  this  idea  for  studying  the  relation  between 
reaction  velocity  and  concentration  of  aromatic  nitro-bodies. 

If  the  maximum  current  strength  at  which  no  hydrogen 
is  yet  evolved  is  designated  •  by  Jm,  the  concentration  of  the 
body  to  be  reduced  by  C,  the  experimental  equation  resulted 


•C*  is  the  concentration  of  a  cross-section,  i.e.  the  reaction 
takes  place  directly  at  the  electrode  surface.  If  we  suppose 
that  the  adjustment  of  the  equilibrium  takes  place  there  with 
extreme  rapidity,  according  to  Nernst,  then  the  reaction  velocity 
will  have  to  be  based  solely  on  the  diffusion  velocity,  and  will, 
therefore,  be  directly  proportional  to  the  concentration  of  the 
depolarizer  in  the  electrolyte.  The  theory  hence  demands  the 
formula 

Jm=K-C. 

1  Ztschr.  f.  Elektrochemie,  7,  263  (1900). 


THEORETICS.  33 

The  lack  of  conformity  has  not  yet  been  explained.  Perhaps 
the  supposition  of  a  very  rapid  attainment  of  the  equilibrium 
at  the  electrode  does  not  apply  to  the  reduction  of  nitrobenzene, 
which  abounds  in  phases. 

The  results  of  Akerberg l  concerning  the  velocity  of  the 
electrolytic  decomposition  of  oxalic  acid  in  the  presence  of 
sulphuric  acid  agree  better  with  the  theoretic  requirements. 
So  long  as  the  proportion  of  oxalic  acid  is  considerable,  the 
decomposition  takes  place  according  to  Faraday's  laws,  i.e. 
without  evolution  of  oxygen.  But  if  the  solution  has  reached 
a  certain  dilution,  the  electrolysis  occurs — independently  of 
.the  current  density — accompanied  by  an  evolution  of  oxygen 
proportional  to  the  concentration  of  the  oxalic  acid  in  the 
solution.  The  decomposition  of  the  oxalic  acid  then  takes 
place  in  the  same  proportion  as  new  oxalic  acid  diffuses  from 
the  electrolyte  to  the  electrode  boundary  surface.  Conse- 
quently, according  to  Nernst's  theory,  the  electrolytic  oxida- 
tion velocity  henceforth  becomes  a  diffusion  velocity. 

The  hypothesis  of  the  latter  is  always  the  instantaneous 
equilibrium  at  the  contact  surface  of  heterogeneous  phases; 
but  the  fulfillment  of  this  condition  is  not  to  be  accepted  forth- 
with, particularly  in  the  cas"e  of  many  organic  processes  which 
—for  instance,  the  reduction  of  nitro-bodies — are  able  to  give 
a  whole  series  of  intermediate  phases  up  to  the  final  equilibrium. 

The  influence  of  the  electrode  material  upon  the  velocity 
of  reaction  decides  particularly  against  its  significance  in  all 
cases  as  a  diffusion  velocity. 

Finally,  to  view  electrolytic  processes  as  heterogeneous  sys- 
tems does  not  seem  at  all  sound,  according  to  the  description 
of  the  electrochemical  reaction  .mechanism  given  in  our  intro- 
duction. If  the  first  process,  in  accordance  with  the  given 
exposition,  is  the  discharge  in  the  electrode  boundary  surface, 
and  if  the  second  is  the  separation  on  the  electrode  or  the 


1  Ztschr.  f.  anorg.  Chemie  31,  161  (1902).  See  also  Brunner,  Reaction 
Velocities  in  Heterogeneous  Systems,  p.  52.  Thesis,  Gottingen,  1903.  Cf. 
also  Luther  and  Brislee,  Ztschr.  f.  phys.  Chemie  45,  216  (1903). 


34  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

reaction  of  the  ions  present  in  the  boundary  surface  with  the 
depolarizer,  hence  in  the  fluid  system,  then  the  actual  reaction 
takes  place  in  a  homogeneous  system.  The  typical  influence  of 
the  reacting  ions  will  then  show  itself  in  the  velocity  constant 
of  this  reaction;  likewise,  if  the  ions  are  derived  from  the  lat- 
ter, the  typical  effect  of  the  electrode  metal  will  be  seen. 
A  sharp  distinction  will  then  exist  between  the  discharge,  which 
can  occur  with  an  extremely  great  velocity,  and  the  actual  chem- 
ical reaction  with  the  depolarizer,  the  velocity  of  which  will  be 
measurable  and  distinctly  individualistic.  In  this  case  the 
velocity  of  diffusion  alone  cannot  represent  the  velocity  of 
reaction. 

With  the  aid  of  other  ideas  concerning  the  electrical 
reaction  mechanism,  particularly  the  reduction  mechanism, 
Haber  and  Russ1  arrive  at  the  same  interpretation.  They 
advance  the  proposition:  "The  reducing  phase  is  formed 
at  the  cathode  with  an  immeasurably  great  velocity  constant, 
but  the  velocity  with  which  it  acts  chemically  on  the  depolarizer 
depends  upon  the  latter 's  peculiarities  and  is  often  measur- 
ably small." 

By  a  "  reducing  phase"  is  meant  hydrogen  or  any  metal 
phase  which  is  supposed  to  stand  in  a  dynamic  equilibrium 
with  it,  so  that  the  action  of  the  different  cathode  materials 
can  be  taken  as  equal,  a  condition  which  can  be  experimentally 
obtained  by  the  choice  of  a  cathode  potential  which  remains, 
always  the  same. 

~b.  Osmotic  Theory  of  Electrical  Reduction. 

Haber  2  was  the  first  to  publish  a  theory  of  electrical  reduc- 
tion which  is  in  many  points  free  from  the  limiting  conditions 
of  the  diffusion  theory.  Later,  conjointly  with  Russ,3  he 
brought  it  to  the  form  given  below. 


1  Ztschr.  f.  phys.  Chemie  47,  263  (1904). 

2  Ibid.  32,  193  (1900). 


3  Ibid.  47,  263  (1904). 


THEORETICS.  35 

The  sphere  of  validity  of  this  theory,  in  conformity  with 
the  experimental  material,  extends  to  the  use  of  unattackable 
cathodes  at  current  strengths  which,  in  contradistinction  to 
those  chosen  by  Goldschmidt,  lie  considerably  below  those 
necessary  for  developing  hydrogen.  The  conditions  are  hereby 
simplified,  because,  on  the  one  hand,  the  reduction  must  pro- 
ceed exactly  according  to  Faraday's  laws,  and,  on  the  other 
hand,  it  can  be  regarded  as  being  always  accomplished  by 
the  same  agent,  hydrogen.  This  latter  hypothesis,  since  it  per- 
mits the  assumption  that  the  reducing  agent  obeys  the  laws 
of  gases,  is  extremely  weighty  for  the  theory.  Herewith  is 
assumed  that  the  hydrogen  is  present  in  the  electrode  surface 
with  the  concentration  C#.  If  we  want  to  assume  the  re- 
placement of  the  hydrogen  by  a  metal,  the  latter  must  also  be 
regarded  as  obeying  the  laws  of  gases.  It  hence  suffices  to 
deduce  the  theory  only  for  hydrogen  as  a  reducing  agent.  If 
CH'  be  the  concentration  of  the  hydrogen  atoms  at  the  cathode, 
then  the  potential  E,  according  to  Nernst's  osmotic  formula,  is 


in  which  R  is  the  gas  constant,  and  T  the  absolute  temperature. 
If  the  hydrogen  in  the  cathode  now  reacts  with  the  depolar 
izer  M,  for  instance  according  to  the  equation 

M+2H'+2E®=M+H2  = 
the  speed  of  reduction  is 


or,  neglecting  the  sub  tractive  member, 

dCM 


According    to    the    above-mentioned  hypotheses,   we    can 
directly  substitute  the  current  strength  J  for  the  speed,  which 


36  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

is  proportional  to  it, 

dCM    ,   , 
•~A  =klJ' 

=C2H    or,  more  simply,     p7f^  =  02H, 


If  this  value  is  introduced  into  the  potential  equation, 


there  results 

~  2 


or  if  CH-  is  considered  as  constant,  and  the  constant  kf  is  placed 
in  the  formula  as  subtractive  member, 

RT.    J 

E  =-x-ln79 — const. 
2      CM 

The  relations  were  now  tested  for  the  constant  J  in  an 
alcoholic  nitrobenzene  solution;  as  a  result  the  formula  can  also 
be  written  in  the  following  manner: 

RT.         1 

E  =-7pln^ const. : 


furthermore,  for  constant  nitrobenzene  concentration, 

73  m 

E  =-jr-lnJr  —  const., 

« 

and  finally  for  constant  cathode  potential,   the  relation 
~ =  const. 


So  far  as  a  logarithmic  connection  between  E  on  the  one 
hand,  and  J  and  CM  on  the  other  resulted,  the  theory  is  veri- 


THEORETICS.  37 

fied  by  the  observation.    However,  the  constant  factor  before 

D/Tf 

the  logarithm  was  not  found  at  —~-.    It  always  possessed  a 

larger  and  somewhat  variable  value. 

Haber  and  Russ  l  therefore  changed  the  original  formula  to 


(RT1    J        +  \ 

\  ~2~      C const- )  • 


This  expression  was  substantiated  by  experience  when  the 
influences  of  diffusion  were  avoided  as  much  as  possible.  The 
factor  x  appears  as  a  function  of  the  electrode  condition 

It  would  lead  too  far  to  enlarge  upon  the  meanings  of  the 
factor  x  which  were  discussed  by  Haber  and  Russ.2 

c.  Summary  of  the  Theories. 

The  two  theories  of  Nernst  and  Haber  above  mentioned  seem 
to  contradict  one  another  in  important  points.  The  electrical 
speed  of  reaction  in  the  diffusion  theory  (Nernst)  is  directly  a 
speed  of  diffusion;  Haber's  formula  holds  good  only  in  case  the 
diffusion  is  excluded  as  much  as  possible. 

The  contradiction  is  only  an  apparent  one,  and  the  difference 
between  the  theories  lies  in  the  hypotheses.  The  measurement 
of  the  speeds  of  reaction  depends  upon  the  conditions  of  the 
experiment.  If  the  reaction  between  two  components  of  re- 
action actually  takes  place  instantaneously,  we  can  vary  the 
time  of  reaction  entirely  at  will  by  the  period  of  time  during 
which  we  add  one  of  the  components.  If  the  latter  is  used  up 
with  immeasurable  rapidity,  the  measured  velocity  of  reaction 
must  naturally  always  remain  proportional  to  the  added  quan- 
tity of  the  reaction  components.  The  Nernst  theory  is  based  on 
relations  in  which  this  subsequent  delivery  is  effected  only  by  the 
diffusion,  the  reacting  agent  furnished  by  the  current  being 

1  Ztschr.  f   phys.  Chemie  47,  264  (1904). 

2  Cf .  also:   Russ,  Concerning  Reaction  Accelerations  and  Reaction  Retar- 
dations in  Electric  Reductions  and  Oxidations.     Ztschr.  f.  phys.  Chemie  44, 
641  (1903).     See  also  the  chapter  on  electrode  material. 


.38  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

kept  at  the  electrode  by  the  potential  relations  in  an  infinitesi- 
mal concentration  as  opposed  to  the  external  concentration. 
Since  the  reaction  can  only  proceed  further  if  new  quantities 
of  the  agent  reach  the  electrode,  and  this  subsequent  delivery 
can  be  brought  about  only  by  transference  and  diffusion,  the 
first  conclusion  drawn  is  that  these  two  factors  determine 
the  current  strength.  The  current  can  reach  the  electrode 
only  by  means  of  ions.  Since,  moreover,  the  measurable 
velocity  of  reaction  is  regulated  by  the  current  strength,  it 
follows  further  that  this  velocity  of  reaction  is  also  regulated 
by  the  effects  of  diffusion  and  transference.  It  is  mentioned 
in  Ackerberg's  experiments  what  the  ratios  are  in  the  presence 
of  a  depolarizer.  The  theory  holds  good  if  the  measurable  speed 
of  reaction,  which  need  not  be  identical  with  the  actual  velocity, 
is  artificially  made  a  diffusion  velocity.  The  considerations  of 
Haber  suppose  that  the  ions  and  depolarizer  are  in  such  great 
concentrations  at  the  electrode  that  the  ions  derived  from  the 
great  surplus  bring  about  the  reaction  in  accordance  with  the 
current  strength — independently  of  that  which  is  subsequently 
delivered  by  diffusion.  The  relations  of  Haber  are  therefore 
valid  only  in  such  cases  where  impoverished  phenomena  are 
excluded  at  the  cathode.  Those  of  Nernst  are  true  only  in 
such  where  complete  impoverishment  exists,  i.e.,  where  almost 
zero  concentration  of  the  depolarizer  is  created  at  the  direct 
border  line  of  reaction.  For  the  reaction  can  progress  only 
in  this  case  in  the  same  .proportion  as  the  depolarizer  enters 
by  diffusion  into  the  reaction  layer. 

We  easily  obtain  results  having  the  advantage  of  better 
proof,  if  we  base  the  reaction-kinetic  speculations  upon  the 
views  developed  on  the  reaction  mechanism,  according  to 
which  the  discharge  of  the  ions  at  the  electrode  is  strictly  to 
be  distinguished  from  the  separation  on  the  electrode  or  the 
reaction  with  the  depolarizer.  This  kind  of  proof  is  naturally 
of  greater  significance  for  the  Haber  than  for  the  Nernst  deduc- 
tions. For  even  if  the  whole  reaction,  according  to  our  sup- 
position, takes  place  in  the  fluid  phase,  i.e.  in  a  homogeneous 
.  system,  the  principles  of  the  reaction  can  practically  be  appli- 


THEORETICS.  39 

cable  in  heterogeneous  systems.  In  the  localization  of  the  dis- 
charging space  in  the  immediate  vicinity  of  the  electrode, 
the  layer  in  which  the  discharged  ions  are  present  may  be 
considered  as  an  extremely  thin  film  which  behaves  as  a 
heterogeneous  formation  towards  the  electrolyte.  The  con- 
centration of  the  discharged  ions  in  this  film  is  undoubtedly 
extremely  small  at  the  great  velocity  of  reaction  with  which 
they  separate  or  react.  Thus  the  progress  of  the  reaction 
depends  upon  the  velocity  with  which  diffusion  and  transference 
conduct  new  ions  to  this  film.  If  the  concentration  of  the  de- 
polarizer is  strong,  only  the  last-mentioned  factors  will  influence 
the  reaction  velocity ;  if  it  is  weak,  the  quantity  of  the  depolar- 
izer, which  is  supplied  by  diffusion,  plays  an  important  part. 

Our  views,  that  the  laws  of  gases  can  actually  be  applied 
to  the  concentration  of  the  discharged  ions,  form  a  desirable 
confirmation  of  Haber's  relations.  For  the  discharged  ions, 
which  are  not  in  or  upon  the  electrode  but  in  the  solution, 
must  have  an  osmotic  pressure  proportional  to  the  concentra- 
tion in  the  discharging  space,  i.e.  the  current  strength,  accord- 
ing to  Haber's  conditions.  The  validity  of  the  laws  of  gases, 
if  we  suppose  a  solid  solution  of  the  ions  in  the  electrode,  is 
difficult  to  explain,  particularly  if  the  case  is  one  of  metal  ions 
which  reach  the  cathode  and  there  produce  reduction  effects. 
The  deductions  of  Haber  remain  unchanged  formally,  but  their 
sphere  of  validity  appears  enlarged,  however,  since  under  the 
necessarily  limited  conditions  the  behavior  of  attackable 
cathodes  becomes  also  theoretically  represen table.  A  repe- 
tition of  these  deductions,  however, will  not  be  given  here. 

The  theoretical  treatment  of  the  physicochemical  material, 
which  organic  chemistry  places  so  abundantly  at  our  command, 
is  yet  in  its  initial  state.  Not  only  do  the  many  obscure  points 
incite  to  a  continuation  of  the  work,  but  the  few  results  and 
the  numerous  problems  rather  justify  the  opinion  that  the 
phenomena  of  organic  electrolysis  are  especially  adapted  to 
carry  the  teachings  of  physical  chemistry  into  the  domain 
of  organic  chemistry. 


CHAPTER   II. 
METHODICS. 

IT  is  assumed  that  the  reader  is  familiar  with  the  general 
arrangements  of  electrochemical  experiments.  In  the  follow- 
ing pages  only  those  particulars  will  receive  attention  which 
are  of  special  importance  in  the  electrolysis  of  organic  com- 
pounds. The  arrangement  which  permits  the  observation  of 
the  decisive  potentials,  and  their  control  and  maintenance  at 
a  constant,  is  particularly  important.  Of  importance  are 
certain  electrolyzing  apparatus  suitable  for  particular  pur- 
poses, and  also  arrangements  for  stirring,  which  often  de- 
cisively influence  the  course  of  an  experiment. 

1.  THE  CELLS. 

Cells  of  the  most  varied  constructions,  depending  upon 
the  problem  in  hand,  are  required.  The  conductivity  of  the 
electrolyte,  the  necessity  of  collecting  gases,  the  separation 
of  the  cathode  and  anode  chambers,  regulation  of  the  tem- 
perature, the  variation  of  the  size  of  the  electrode,  all  demand 
certain  requirements  and  arrangements. 

Of  course,  the  comprehensiveness  of  the  experiment  is  also 
of  great  importance.  However,  only  the  conditions  which  enter 
into  the  question  of  scientific  investigations  are  of  interest 
here.  We  shall,  therefore,  waive  the  repetition  of  the  technical 
arrangements  for  organic  electrochemical  processes. 

In  the  simplest  case  it  suffices  to  immerse  the  two  electrodes 
always  in  a  certain  position  in  a  glass  vessel,  and  usually 
parallel  to  one  another.  '  The  vessel  is  closed  with  a  hermetic- 
ally fitting  stopper  when  gases  are  to  be  collected.  Three 

40 


METHODICS.  41 

perforations  are -required  in  the  stopper,  one  for  a  glass  tube, 
and  the  other  two  for  the  electrodes,  the  latter  being  sealed  in. 
A  little  mercury  closes  the  circuit.  Changes  in  temperature 
are  obtained  by  outwardly  heating  or  cooling  the  vessel. 
Stirring  is  caused  by  the  electrolytically  evolved  gases. 

The  current  conditions  can  be  varied  in  the  most  different 
ways.  By  a  choice-  of  concentrations,  or  by  additions,  the  con- 
ductivity can  be  increased  or  diminished;  also  by  raising  or 
lowering  the  voltage.  The  height  of  the  electromotive  force 
developed  in  the  cell  determines  the  current  strength ;  the  ratio 
of  the  latter  to  the  electrode  surfaces  gives  the  current  density, 
and  to  the  volume  of  the  electrolytes,  the  current  concentra- 
tions.1 

This  simplest  form  of  arrangement  seldom  suffices;  usually 
a  separation  of  the  cathode  and  anode  spaces  is  required. 
This  is  of tenest  obtained  by  the  use  of  a  diaphragm, .  or  by 
connecting,  with  a  siphon  arrangement,  two  separate  vessels, — 
one  containing  the  anode  and  the  other  the  cathode  fluid; 
this  latter  method  is  more  rarely  used,  however,  because  the 
resistance  is  liable  to  become  too  great.  Porous  earthenware 
cylinders  or  plates  are  usually  employed  as  diaphragms. 
Diaphragms,  which  often  answer  well,  are  sometimes  made 
of  gypsum,  pressed  asbestus  (only  utilizable  in  alkalies 2), 
porous  cement,  and  parchment  paper.  So-called  "acid-proof" 
diaphragms  are  also  used.  Cylindrical  vessels  are  simply  placed 
in  the  wider  outer  vessel,  and  plates  are  fitted  in  tightly,  or 
cemented  in.  A  simpler  method  is  to  make  the  cell  of  two  sep- 
arate parts  fitting  upon  one  another.  Between  these  the  di- 
aphragm plate  is  tightly  wedged  with  screws  by  means  of  a 
rubber  ring  or  a  caoutchouc  frame.  The  Wehrlin  3  cell  is  made  in 
this  fashion.  Cooling  and  stirring  in  electrolytical  experiments 
are  of  special  importance.  .  Aside  from  the  external  cooling 
of  the  electrolyte,  a  constant  temperature  of  the  latter  can 

1  Tafel,'  Ztschr.  f.  phys.  Chem.  34,  201  (1900). 

2  LeBlanc,  Ztschr.  f.  Elektrochemie  7,  290  (1901). 

3  Ibid.  3,  450  (1897). 


42 


ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 


be  obtained  by  putting  in  glass  or  porcelain  worms  through 
which  a  continuous  current  of  water  is  conducted.  Metallic 
worms  must  only  be  used  if  they  are  to  serve  at  the  same  time 
as  electrodes.  Otherwise  they  act  in  an  undesirable  manner  as 
intermediate  conductors  in  the  electrolysis.  Often  it  is  impor- 


FIG.  1. — Arrangement  for  Cooling  the  Electrodes. 

tant  to  keep  the  electrodes  cool,  since  their  surfaces  limit  the 
actual  reaction  space. 

Cooling  of  the  electrodes  is  done  either  by  using  worm 
electrodes,  as  above  mentioned,  or,  jf  this  is  made  impossible  by 
the  nature  and  form  of  the  electrodes,  by  choosing  hollow,  cy- 
lindrical electrodes, — through  which  water  is  passed, — and  of 


METHODICS. 


43 


the  shape  first  proposed  by  Lob  1  and  later  modified  by  Tafel.2 
Figs.  1-4  represent  types  of  electrolytic  cells  variously  employed. 

It  is  evident  from  the  drawings  that,  by  choosing  suitable 
diaphragms,  the  reaction  chambers  can  be  closed  from  without. 

In  using  earthenware  cylinders,  the  reaction  fluid — anodic 
or  cathodic — is  most  suitably  placed  in  the  earthenware  cylinder, 
especially  if  the  gases  are  to  be  determined. 


FIG.  2.— Tafel's  Electrolytic  Cell.  FIG.  3.— Wehrlin's  Cell. 

Gas  or  mechanical  stirrers  are  made  use  of  for  stirring  the 
electrolyte.  Mechanical  stirrers,  however,  are  employed  only  if 
the  electrolytic  gases  are  to  be  investigated,  unless  these  suffice 
for  the  stirring,  as  is  the  case  in  experiments  with  high  cur- 
rent strengths.  By  permitting  the  base  of  the  stirrer  to  dip 
into  mercury,3  the  mechanical  stirring  can  easily  be  arranged 
in  a  manner  so  as  to  obtain  a  hermetical  seal. 

1  Ztschr.  f.  Elektrochemie  2,  665  (1896). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  33,  2223  (1900). 

3  Lob,  Ztschr.  f.  Elektrochemie  7,  117  (1900);   Ztschr.  f.  phys.  Chemie  34, 
647  (1900). 


44 


ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 


The  gas-tight  electrode  stirrers  are  based  on  the  same 
principle.  They  have  the  advantage  of  using  the  electrodes 
themselves, — which  may  have  any  shape, — for  stirring.  A 
fine  division  of  the  components  is  thus  assured  on  the  elec- 
trode surface  the  (reaction  space).  This  matter  is  of  great  im- 
portance in  a  series  of  reactions,  for  instance  in  the  simultane- 

•  To  Current 


land 


FIG.  4.— Electrolytic  Cell  (Hofer's) 


FIG.  5. — Gas-tight  Electrode 
Stirrer. 


ous  reduction  of  two  nitro-bodfes  to  a  mixed  azo-body,   or 
in  the  electrolytic  preparation  of  azo-dyes,  etc.     (See  Fig.  5.) 
The  current  is  conducted  through  mercury,  which  is  poured 
into  the  glass  tube  in  which  the  electrode  is  sealed. 

2.   ARRANGEMENT   OF   EXPERIMENTS  AND    MEASUREMENTS  OF 

POTENTIAL. 

The  typical  arrangement  for  an  electrical  decomposition  is 
that  in  which  the  main  current  flows  through  an  ammeter  and  the 


METHODICS.  45 

cell,  and  the  terminals  of  a  voltmeter,  in  branch  circuit,  are 
connected  directly  to  two  points  at  the  electrodes. 

The  potential  of  the  electrode  at  which  the  respective 
reaction  takes  place  is  of  decisive  importance  on  the  course  of 
the  electrolysis;  it  may  be  the  cathode  or  anode  potential  or 
sometimes  both.  The  potential  difference  between  the  elec- 
trodes, which  is  influenced  by  many  contingencies,  such  as 
the  resistance  of  the  diaphragm,  etc.,  is,  on  the  contrary, 
generally  without  importance  for  the  reaction.  The  volt- 
meter shows  the  consumption  of  electrical  energy  only  in  com- 
bination with  the  ammeter. 

The  potential  of  an  electrode  is  determined  in  combination 
with  a  second  constant  electrode  which  does  not  belong  to 
the  actual  electrolytic  system.  This  subsidiary  or  standard 
electrode,  whose  potential  is  either  arbitrarily  taken  as  zero 
or  has  a  certain  absolute  value,  is  connected  by  a  siphon  with 
the  liquid  surrounding  the  experimental  electrode.  The  electro- 
motive force  of  this  galvanic  combination  is  then  measured 
by  one  of  the  well-known  methods,  with  a  galvanometer 
or  capillary  electrometer.  If  the  potential  difference  of  the 
standard  electrode  is  correctly  subtracted  from  the  obtained 
value,  the  difference  in  potential  of  the  reaction  electrode, 
based  on  the  agreed-upon  zero)  value  of  the  potential,  is 
obtained. 

Two  subsidiary  or  standard  electrodes  are  in  use,  the  calo- 
mel electrode  of  Oswald l  and  the  hydrogen  electrode  of 
Nernst.2  The  former,  consisting  of  a  combination  of  mercury 
covered  with  mercurous  chloride  as  depolarizer  and  immersed 
in  a  solution  of  Vio  n-potassijim-chloride  solution,  has,  accord- 
ing to  the  best  measurements,  an  absolute  potential  of 
0.613  volt +0.0008  (t°-18),  in  the  sense  that  mercury  is  posi- 
tive, the  solution  negative.  The  standard  hydrogen  electrode 

1  Ostwald-Luther,  Physicochemical  Measurements,  p.  383,  Leipzig,  1902. 

2Ztschr.  f.  Elektrochemie  4,  377  (1898);  7,  253  (1900);  see  also  Wils- 
more,  Ztschr.  f.  phys.  Chem.  35,  291  (1900);  Ostwald-Wilsmore,  Ztschr.  f. 
phys.  Chem.  36,  91  (1901). 


46  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

consists  of  a  platinum  sheet  charged  with  hydrogen  in  a  normal 
electrolyte,  i.e.  normal  as  to  the  hydrogen  ions.  In  preparing 
the  hydrogen  electrode,  the  sheet  platinum  (or  palladium) 
is  arranged  so  as  to  lie  half  in  the  electrolyte  and  half  in 
hydrogen  gas,  and  the  saturated  state  is  maintained  by 
having  a  constant  current  of  hydrogen  pass  through  the 
electrolyte.  The  half  of  the  electrode  not  in  the  electrolyte 
must  thus  be  surrounded  during  the  entire  time  of  the  ex- 
periment by  an  atmosphere  of  hydrogen.  Nernst  gives  the 
hydrogen  electrode  the  arbitrary  value  0. 

Depending  upon  the  form  of  the  cell,  the  connection  with 
the  standard  cell  can  be  made  by  means  of  a  siphon  or  other 
method.  Of  course  the  electrolyte  of  the  normal  electrode 
must  not  react  appreciably  with  that  of  the  experimental 
cell,  and  hi  most  cases  it  will  be  of  value  to  separate  both  by 
a  suitably  adjusted  diaphragm. 

The  problems  to  which  the  measurement  of  the  electrode 
potential  gives  rise  are  manifold. 

The  task  is  often  to  determine  at  what  potential  a  reaction 
begins;  in  other  words,  what  discharge  potential  the  separated 
or  reacting  ion  possesses  in  the  presence  of  the  depolarizer. 
The  determination  of  this  value  is  most  simply  made  by  measur- 
ing the  decomposition  potential.1  This  method  is  based  upon 
the  fact  that  a  permanent  decomposition  of  an  electrolyte  can 
only  take  place  by  using  a  certain  electromotive  force  which 
is  just  able  to  overcome  that  of  the  polarization.  If  we  begin 
to  polarize  with  a  small  electromotive  force,  the  current  cannot 
at  first  permanently  pass  the  cell.  Only  when  the  electro- 
motive force  exceeds  the  value  of  the  polarization  does  the 
sudden  deflection — the  "rebound"  of  a  galvanometer  enclosed 
in  the  circuit  for  observation — show  the  passage  of  the  current, 
revealing  the  decomposition  value  of  the  electrolyte.  If  in  a 
coordinate  system  the  electromotive  forces  are  considered  as 
abscissas,  the  current  strengths  or  deflection  factors  of  the  gal- 
vanometer as  ordinates,  then  curves  are  obtained  which  show 

JLe  Blanc,  Ztschr.  f.  phys.  Chem.  8,  299  (1891);    12,  333  (1893). 


METHODICS.  47 

characteristic  breaks  at  the  decomposition  values.  If  the  elec- 
trode at  which  the  reaction  is  expected  to  occur  is  combined 
with  a  normal  electrode,  and  the  difference  in  potential  at  the 
work-electrode  is  observed  for  increasing  current  strengths,  it 
will  be  found  that  at  a  certain  value  of  the  latter,  a  sudden 
passage  of  the  current,  which  appears  as  a  break  in  the  curve, 
occurs.  This  break  is  characteristic  for  the  beginning  of  any 
kind  of  reaction,  whether  it  be  that  of  the  separation  of  ions 
or  their  reaction  with  the  depolarizer.  When  several  kinds  of 
ions  are  separated  or  react  at  different  electromotive  forces,1 
these  breaks  can  repeat  themselves  in  the  curve. 

The  simplest  method  of  determining  the  beginning  or  non- 
occurrence  of  a  reaction  consists  in  measuring  the  discharge 
potential  of  the  cations  or  anions  before  and  after  the  addition 
of  the  depolarizer  which  is  to  be  acted  upon.  A  change  in 
potential  at  the  addition  shows  the  beginning  of  the  reaction. 

It  is  of  especial  importance  to  know  the  potential  interval 
within  which  one  or  several  distinct  reactions  take  place.  The 
determination  of  this  depends  upon  the  change  in  potential 
which  the  presence  of  a  depolarizer  produces  as  opposed  to 
an  electrolyte  containing  no  depolarizer.  For  example,  if  it  is 
desired  to  learn  if  chlorine  derivatives  of  phenol  can  be  pre- 
pared at  the  anode  by  electrolysis  of  a  hydrochloric-acid  solu- 
tion of  phenol,  then  the  point  of  decomposition  of  the  chlo- 
rine ion,  in  combination  with  the  hydrogen  electrode,  is  found 
at  1.31  volts  in  a  Vi  n-hydrochloric-acid  solution.  If  phenol 
is  added  to  this  solution,  the  break  in  the  curve  occurs 
already  at  0.9  volt.2  Therefore  the  span  in  potential,  within 
which  the  reaction  for  the  formation  of  chlorine  derivatives 
of  phenol  must  take  place,  lies  between  0.9  and  1.3  volts.  In 
this  manner  Dony-Henault,  among  others,  determined  the 
decomposition  potential  of  the  OH  ions,  in  combination  with 
the  hydrogen  electrode,  in  dilute  sulphuric-acid  solution  both 
without  and  with  the  addition  of  ethyl  alcohol.  He  found 

~S.  Glaser,  Ztschr.  f.  Elektrochemie  4,  355,  373,  397  (1897);   Bose.  ibid' 
5, 153  (1898). 

2Cf.  Dony-Henault,  Ztschr.  f.  Elektrochemie  6,  533  (1900). 


48 


ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 


in  the  first  case  that  the  discharge  potential  was  at  1.66 
volts,  in  the  second  case  at  about  1.2-1.3  volts.  Either 
acetaldehyde  or  acetic  acid  can  be  formed  by  the  action  of 
hydroxyl  ions  upon  alcohol.  A  measurement  of  the  decom- 
position potential  of  the  hydroxyl  ions  in  dilute  sulphuric  acid 
and  in  the  presence  of  acetaldehyde  did  not  perceptibly  lower 
the  potential.  The  acetaldehyde,  under  the  existing  circum- 
stances, does  not  act  as  a  depolarizer,  so  that,  if  the  potential 
during  electrolysis  is  kept  between  1.3-1.6  volts,  an  almost 


FIG.  6. — Arrangement  of  Experiment  (Haber). 

quantitative   yield  of  acetaldehyde   must   be   obtained.    The 
experiments  completely  verified  this  theoretical  deduction. 

The  second  problem,  which  often  occurs,  is  to  keep  this 
potential   at  a   certain  value,  or   within  certain  limits.      This 


METHODICS.  49 

is  accomplished  by  setting  the  cell,  which  consists  of  the 
work-electrode  and  the  normal  electrode,  at  the  desired  ten- 
sion by  choosing  the  suitable  polarizing  current  strength- 
according  to  the  compensation  method, — and  by  taking  care 
that  the  tension  existing  between  the  work  electrode  and 
the  standard  electrode  retains  the  value  of  the  compensating 
potential  by  varying  the  current  strength  as  may  become 
necessary  during  the  course  of  the  experiment.  Haber  1  has 
used  this  method  of  procedure  for  limited  potentials,  and  Lob 
and  Moore 2  employed  it  for  an  entirely  distinct  constant 
potential  during  prolonged  electrolyses.  Figs.  6  and  7  are 
sketches  of  the  arrangements  of  their  experiments.  The 
requirements  for  the  reduction  of  nitrobenzene,  as  expressed 
in  the  theoretical  part  of  this  book,  were  proved  by  these 
experiments, — namely,  that,  by  reason  of  the  necessary  limi- 
tations, only  the  cathode  potential  is  decisive  for  the  obtainable 
reduction  phase. 

If  in  simpler  cases,  which  are  naturally  rarer  in  organic 
electrolysis,  the  only  point  is  to  keep  the  total  decomposition 
tension  between  the  electrodes  below  a  certain  value,  then 
it  will  suffice  to  employ  suitably  small  electromotive  forces, 
or  such  limited  by  branching. 

Finally,  the  measurement  of  single  electrode  potentials  is 
of  importance  in  itself  for  obtaining  the  depolarizing  values, 
i.e.,  the  potential  differences  of  an  electrolyte  in  connection  with 
a  certain  electrode  with  or  without  a  depolarizer.  It  is  evident 
that  these  depolarizer  values  are  characteristic  quantities  for 
the  chemical  nature  of  the  depolarizer,  and  are  very  closely 
related  to  the  constitution  and  configuration  of  the  molecule. 
Introductory  experiments  on  this  question  for  nitro-  and  nitroso- 
bodies  have  been  made  by  Panchaud  de  Bottens.3  Lob  and 
Moore  4  have  also  measured  the  depolarizing  values  for  nitro- 
benzene at  different  electrodes  and  current  strengths.  It  was 

1  Ztschr.  f.  Elektrochemie  4,  507  (1898). 

2  Ztschr.  f.  physik.  Chem.  47,  432  (1904). 
Ztschr,  f.  Elektrochemie  8,  305,  332  (1902). 

*  Ber.  d   5.  Internat.  Kongr.  f.  angew.  Chemie,  Berlin,  1903,  4,  666. 


50 


ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 


found  that  they  generally  became  smaller  with  increasing 
current  strengths.  Single  electrode  metals,  however,  show 
peculiarities  which  suggest  the  occurrence  of  variable  reactions. 
Besides  the  usual  method  of  arrangement  mentioned  at  the 
beginning  of  this  chapter,  in  which  the  current  derived  from 
any  suitable  source  of  electricity  passes  through  the  cell, 
the  apparatus  can  often  be  suitably  simplified — especially 
for  electrical  reductions — by  employing  Lob  reaction  cells1 


Main  Current :  -  —  A  Current  Source,  B  Rheostat,  C  Ammeter,  D  Anode,  E  Cathode, 

F  Plate  Resistance,  Z  Experimental  Cell. 

Measuring  Current: A'  Compensation  Accumulators,  B'  Precision  Voltmeter,  C'  Plate 

Resistance,  D'  Ballast  Resistance,  E'  Galvanometer,  F'  Instan- 
taneous Cutout,  G  Standard  Electrode. 

FIG.  7. — Lob's  Experimental  Arrangement 

or  short-circuiting  cells.  Cells  can  be  constructed,  which  do 
away  with  the  primary-current  production  in  laboratory 
work,  based  upon  the  fact,  already  used  by  Royer 2  in  the 
reduction  of  oxalic  acid,  that  a  reaction  producible  by  the 
current  can  inversely  serve  as  a  part  of  a  suitably  constructed 
electric  cell.  If,  for  instance,  nitrobenzene  is  dissolved  in  con- 
centrated sulphuric  acid,  the  solution  poured  into  an  earthen 
ware  cylinder,  a  piece  of  platinum  dipped  in  the  latter  and  the 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  1390  (1896). 
2Compt.  rend.  69,  1374  (1869);    see  also  LapeyriSre,  Tommasi,  Traite* 
d'Electrochimie  724,  729  (1899). 


METHODICS.  51 

cylinder  with  its  contents  placed  in  another  vessel  containing  di- 
lute sulphuric  a'cid  in  which  is  immersed  a  piece  of  amalgamated 
zinc,  we  have  an  electric  cell  or  battery.  On  making  a  metallic 
contact  between  the  zinc  and  platinum  with  a  binding-screw, 
quite  a  considerable  current  circulates  even  at  a  low  tension, 
since  the  resistance  is  small.  After  a  few  hours  the  contents 
of  the  earthenware  cylinder  solidifies,  forming  a  pasty  mass  of 
arnidophenol  sulphate.  Such  systems  can  be  prepared  in  very 
many  suitable  forms,  particularly  in  such  a  manner  that  heat, 
or  pressure,  etc.,  can  be  applied  during  the  operation. 

3.  THE  ELECTRODES. 

The  nature  of  the  electrodes  is  of  great  importance  for  the 
course  of  electrolytic  processes.  The  material  is  not  only 
decisive  for  the  effect,  as  already  fully  discussed,  but  the  nature 
of  the  surface  and  the  previous  treatment  of  the  electrodes 
can  decidedly  influence  the  course  of  the  electrolysis.  In  the 
first  place  it  is  obvious  that  the  size  of  the  surface  wetted  by 
the  electrolyte  is  codeterminative  for  the  potential  and  current 
density,  and  even  on  this  account  its  smoothness  or  roughness 
form  decisive  factors;  but  its  form,  and  the  mutual  position  of 
both  electrodes,  must  also  be  taken  into  consideration,  for  on 
these  depend  the  distribution  of  the  lines  of  force  on  the  surface. 
In  general,  the  data  on  the  current  densities  and  of  the  potentials 
refer  to  mean  values;  actually  both  are  usually  unlike  at  different 
points  of  the  surface,  since  the  number  of  the  discharging 
current  lines  is  an  uneven  one. 

It  is,  therefore,  often  to  be  recommended,  especially  in 
accurate  potential  measurements,  to  "'touch  over"  the  surface. 
Haber  l  does  this  by  shaping  the  siphon  end  of  the  standard 
electrode  into  a  capillary  tube,  which  he  conducts  along  the 
electrode  surface.  If  the  object  is  to  obtain  tolerably  equal 
current  densities  without  this  accurate  checking  of  the  re- 
sults, the  relative  size  and  position  of  both  electrodes  must 

1  Ztschr.  f.  phys.  Chemie  32,  209  (1900). 


52  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

be  taken  into  consideration.  They  may  be  chosen  of  similar 
dimensions  and  like  form,  and  hung  parallel  in  the  bath. 
A  better  way  is  to  choose  concentric  arrangements  such  as 
mentioned  by  Lob  1  and  Tafel.2  These  electrodes  consist  of 
concentric  cylinders  between  which  the  electrolysis  takes  place. 
It  has  already  been  mentioned,  in  the  discussion  on  the  excess 
potential  phenomenon,  in  what  manner  the  nature  of  the-  elec- 
trode potential  is  of  importance  for  the  potential,  leaving  out 
of  the  question  the  changed  dimensions.  The  evolution  of 
hydrogen  is  well-nigh  reversible  at  platinized  platinum  (0.005 
volt  excess  potential) ;  at  bright  (polished)  platinum  it  is  already 
0.09  volt.  This  influence  possibly  occurs  in  a  similar  manner 
with  all  electrode  materials.  Tafei,3  by  reducing  difficultly  re- 
ducible substances  in  sulphuric-acid  solution,  was  able  to  obtain 
good  results  only  at  a  lead  cathode,  the  surface  of  which  was 
coated  with  a  layer  of  spongy  lead.  Such  a  surface  can  easily 
be  prepared  by  first  coating  the  electrode  anodically  with  a  thin 
film  of  lead  peroxide  and  then  reducing  this  cathodically.  Sim- 
ultaneously a  solution  of  the  foreign  metals  in  the  surface  coat  is 
brought  about  by  the  anodic  process  and  a  pure  lead  surface 
obtained  by  reduction.  Tafel,  by  a  great  number  of  examples, 
has  likewise  demonstrated  how  important  it  is  to  have  a  pure 
cathode.  Even  traces  of  impurities  can  decisively  modify  the 
effect.  The  simplest  supposition  is  that  the  velocity  of  separa- 
tion of  the  discharged  ions  is  catalytically  influenced  by  the  traces 
of  impurities.  This  assumption  agrees  best  with  the  experimen- 
tal results.  Indeed,  if  the  reduction  energy  is  lowered  by  the 
impurities,  we  must  conclude  that  an  accelerated  catalytical 
action  of  the  hydrogen  formation  occurs;  this  agrees  with  the 
observation  of  Tafel.  that,  with  a  constant-current  source  and 
outer  resistance,  a  disturbance  of  the  reduction  goes  hand  in 
hand  with  an  increase  oi  the  current,  or,  what  is  the  same 
thing,  a  lowering  of  the  potential  difference  at  the  cathode. 


1  Ztschr.  f.  Elektrochemie  2,  665  (1896). 

2Ber.  d.  deutsch.  chem.  Gesellsch.  33,  2223  (1900). 

3  Ztschr.  f.  phys.  Chem.  34,  187  (1900). 


METHODICS.  53 

Lob  and  Moore  l  have  obtained  the  suitable  surface  con- 
stitution and  purity  of  the  cathode  in  a  different  manner  from 
Tafel.  They  start  with  a  carefully  platinized  platinum  gauze 
electrode  and  coat  this  electrolytically  with  the  desired  metal 
by  electrolyzing  a  pure  salt  solution  under  suitable  conditions. 
They  thus  succeeded,  even  with  attackable  cathodes,  in  ob- 
taining quite  constant  cathode  potentials  for  a  long  period. 

Russ  2  has  observed  a  peculiar  influence  of  the  pretreatment 
of  the  electrodes.  If  strong  currents  are  sent  through  the  cell 
for  a  longer  period,  so  that  an  energetic  evolution  of  hydrogen 
occurs  in  the  presence  of  a  depolarizer,  the  cathode  potential 
soon  drops,  even  if  the  current  remains  constant,  and  the  evolu- 
tion of  hydrogen  ceases.  The  original  potential  and  renewed 
hydrogen  evolution,  after  a  short  interruption  of  the  current, 
reoccurs  when  the  current  is  again  turned  on.  Hence,  the  elec- 
trodes depolarize  better  after  being  charged  with  hydrogen 
than  without  the  latter.  The  extent  of  this  influence  varies 
with  different  metals. 

M.  c. 

2  Ztschr.  f.  phys  Chem.  44,  641  (1903). 


CHAPTER  III. 
ELECTROLYSIS   OF  ALIPHATIC  COMPOUNDS. 

ORGANIC  compounds  which  are  decomposed  in  solution  by 
a  direct  current  can  be  divided  into  those  that  behave  as  elec- 
trolytes and  those  that  act  merely  as  depolarizers.  This 
division  is  not,  however,  altogether  appropriate,  because  both 
effects  often  occur  simultaneously,  so  that  a  strict  carrying  out 
of  this  disposition  is  not  possible  without  arbitrariness  and 
numerous  repetitions.  The  classification  into  oxidation  and 
reduction  processes,  which  proved  practical  in  the  theoretical 
part,  would  also  be  serviceable  in  the  presentation  of  the  ex- 
perimental data,  even  though  anodic  and  cathodic  effects  are 
sometimes  observed  side  by .  side,  or  successively,  in  an  elec- 
trolysis. However,  the  advantages  of  the  latter  division 
are  combined  with  the  greatest  possible  survey  of  the  material 
if  this  is  arranged  only  in  accordance  with  the  chemical  character 
of  the  substances  which  serve  as  the  starting-point.  The 
sequence  of  the  latter  is  prescribed  by  the  familiar  arrange- 
ment employed  in  text-books  on  organic  chemistry.  Moreover, 
the  property  of  depolarizing,  anodically  or  cathodically,  depends 
upon  the  nature  of  the  materials  which  serve  as  the  starting- 
point,  each  group  of  bodies  exhibiting  a  fixity  in  its  electro- 
chemical behavior,  whereby  an  almost  separate  grouping  of 
the  oxidation  and  reduction  processes  naturally  follows. 

1.  CARBON  AND  HYDROCARBONS. 
Carbon. 

Carbon,    the    characteristic    element   of    all    organic    coni 
pounds,  is,  as  such,  also  the  primal  product  in  the  eiectro- 

54 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  55 

synthesis  of  organic  substances.  The  well-investigated  electro- 
thermic  processes  of  carbide  formation  on  the  one  hand,  and, 
on  the  other,  the  little  explained  phenomena  of  the  electrolytic 
solution  of  carbon  by  the  action  of  the  anode  current,  form 
the  introduction  to  these  syntheses.  That  this  solution  occurs 
when  carbon  is  used  as  the  anode  in  an  acid  electrolyte,  has 
been  repeatedly  observed;  likewise  the  frequently  occurring 
presence  of  carbon  in  the  cathode  precipitate  in  galvanic  metal- 
deposition  has  also  been  noted.  In  the  electrolysis  of  dilute 
sulphuric  acid,  using  carbon  electrodes,  Bartoli  and  Papasogli l 
had  found  that  the  anode  carbon  is  attacked,  which  was  shown 
by  the  appearance  of  carbon  mon-  and  dioxide.  Coehn2 
then  demonstrated  that  carbon  goes  into  solution  under  suit- 
able conditions,  coloring  the  sulphuric  acid;  as  a  constituent 
part  of  the  cation  it  wanders  to  the  cathode  and  deposits  itself, 
like  a  metal,  as  a  conductive  coating  upon  the  platinum  cathode. 
The  nature  of  the  solution  (carbon  hydroxide?)  and  of  the  pre- 
cipitate has  not  yet  been  explained.  Coehn  3  was  able,  how- 
ever, to  prove  that  the  solution  of  the  carbon  conforms  to 
Faraday's  law  and  leads  to  the  expected  electrochemical  equiv- 

12 
alent  x  =  3' 

Hydrocarbons. 

The  great  chemical  resistibility  of  aliphatic  hydrocarbons 
and  the  aggregate  state  of  their  members  poor  in  carbon  make 
them  appear  as  unsuitable  material  for  electrolytical  experi- 
ments. Only  the  addition-reactions  of  unsaturated  hydro- 
carbons offer  an  experimental  field.  This  has  not  yet  been 
developed.  These  reactions  are  cathodic  in  the  addition  of 
hydrogen,  and  anodic  in  the  addition  of  halogens,  etc.  The 
fact  that  such  hydrocarbons  occur  in  the  decomposition  of 
aliphatic  acids  gives  us  an  indication  as  to  their  behavior,  which 
will  be  mentioned  at  the  proper  place. 

JGazz.  chim.  14,  90;  15,  461  (1885);  Comp.  rend.  102.  363  (1886). 
2  Ztschr.  f.  Elektrochemie  2,  540,  616  (1896). 
8  Ibid.  3,  424  (1897). 


56  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Acetylene  is  the  only  hydrocarbon  which  has  been  used  as  a 
primal  material. 

Acetylene.  —  Coehn  and  Billitzer  l  have  subjected  acetylene 
to  the  action  of  the  oxidizing  current  in  alkaline  and  acid 
solution  with  limited  anode  potential.  The  discharging  poten- 
tial of  oxygen,  which  is  in  the  neighborhood  of  1.7  volts  in  a 
pure  potassium-hydroxide  solution,  is  lowered  by  acetylene  to 
1.22  volts.  At  this  potential  a  reaction  begins.  It  is  possible 
in  the  same  experiment  to  convert  the  process  into  a  quantita- 
tive one,  if  the  tension  is  kept  between  1.22  and  1.6  volts,  a 
potential  at  which  a  second  reaction  begins,  as  shown  by  the 
sudden  jump  in  the  current  strength.  At  1.35  volts  formic 
acid  is  produced  exclusively,  according  to  the  following  equa- 
tion: 

C2H2  +  6  OH  =  2  H20  +  2  HCOOH. 

In  sulphuric-acid  solution  the  process  proceeds  differently. 
By  conducting  acetylene  into  sulphuric  acid,  aldehyde  is  first 
produced.  This  causes  a  depolarization  of  about  0.19  volt. 
A  quantitative  oxidation  of  the  aldehyde  to  acetic  acid  occurs 
if  the  tension  remains  below  the  discharging  tension  of  oxygen  : 


=  CH3CHO, 
CH3CHO  +  2  OH  =  CH3COOH  +  H20. 

Nothing  is  as  yet  known  regarding  the  reduction  of  acetylene 
and  the  addition  of  halogens. 

2.    NlTRODERIVATIVES   OF  HYDROCARBONS. 

The  reduction  of  aliphatic  nitro-hydrocarbons  in  dilute 
alcoholic  sulphuric-acid  solution  has  been  accomplished  by 
Pierron.2  The  /?-alkyl-hydroxylamines  are  obtained  at  plati- 
num anodes  and  at  a  temperature  of  15°-20°  : 


1  Ztschr.  f.  Elektrochemie  7,  681  (1901). 

2  Bull.  soc.  chim.  [3]  21,  780  (1899). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  57 

and  at  70°-75°  the  amines: 

RNH2+2H20. 


Nitrom  ethane  thus  yields  either  methylhydroxylamine  or 
methylamine.  When  concentrated  hydrochloric  or  sulphuric 
acid  is  used,  hydroxylamine  and  formaldehyde  are  formed,  ie. 
the  decomposition  products  of  an  oxime  which  was  probably 
formed  first  : 


CH3N02  +  2H  =  CH2  :  NOH  +  H20  =  NH2OH+CH30. 

Under  similar  conditions  nitroethane  is  converted  into  /?- 
ethylhydroxylamine  or  ethylamine;  and  n-nitropropane  into 
/?-n-propylhydroxylamine  or  n-propylamine. 

3.  HYDROXYL  COMPOUNDS. 

Oxidation  products  are  principally  to  be  expected  with  the 
aliphatic  hydroxyl  compounds  as  the  lowest  stage  of  oxidation. 
In  fact,  hydrogen  is  evolved  unused,  even  if  the  cathode  and 
anode  are  not  separated  by  diaphragms,  while  the  oxygen  is 
absorbed. 

Methyl  Alcohol.  —  We  are  indebted  to  Renard,1  Almeida 
and  Deherain,2  Jaillard,3  Habermann  4  and  Connell  5  for  numer- 
ous experiments  on  the  electrolysis  of  methyl  alcohol. 

The  results  obtained  with  methyl  alcohol  can  be  summed 
up  as  follows:  Hydrogen  being  evolved,  the  oxidation  products 
formed  are  : 

1.  In  aqueous  sulphuric-acid  solution:  Methyl  formate, 
methylal,  methyl  acetate,  acetic  acid,  and  methyl-sulphuric 
acid,  a  little  carbon  dioxide  and  monoxide,  but  no  formic 
aldehyde. 

1  Compt.  rend.  80,  105,  236  (1875). 

2  Ibid.  51,  214  (1865). 

3  Ibid.  58,  203  (1863). 

4  Monatsch.  7,259(1886). 
5Pogg,  Ann.  36,  487  (1835). 


58  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Renard  considers  the  formation  of  acetic  acid  as  due  to 
reciprocal  action  between  the  alcohol  and  carbon  monoxide: 

CH3OH + CO  =  CH3  -  COOH. 

Jahn  l  thinks  the  formation  must  be  traceable  to  the  presence 
of  ethyl  alcohol. 

2.  In  aqueous  solution,  on  addition  of   potassium  acetate 
(Habermann):    Besides  carbon  dioxide  and  carbon  monoxide, 
methane  and  potassium  methyl-carbonate. 

3.  Without  a  solvent,  by  itself  or  with  the  addition  of  a  little 
alkali:    Chiefly  potassium  carbonate;    also  hydrogen,  oxygen, 
carbon  monoxide,  and  carbon  dioxide. 

While  these  experiments,  which  were  carried  out  without 
giving  a  theoretical  insight  into  the  nature  of  the  electro- 
chemical reaction,  yielded  almost  all  the  possible  oxidation 
products  in  the  oxidation  of  methyl  alcohol,  Elbs  and  Brunner  2 
have  discovered  a  method  which  gives  80%  of  the  current 
yield  in  formaldehyde.  This  is  exactly  the  substance  which 
could  not  be  proven  present  up  to  that  time  among  the  electro- 
lytic oxidation  products  of  methyl  alcohol.  Elbs  and  Brunner 
electrolyzed  an  aqueous  solution  of  160  g.  methyl  alcohol 
and  49  to  98  g.  sulphuric  acid  in  a  litre.  They  employed  a 
bright  platinum  anode  in  an  earthenware  cylinder,  using  a 
current  density  of  3.75  amp.  and  a  temperature  of  30°.  Only 
traces  of  formic  acid  and  carbonic  acid  and  a  little  carbon 
monoxide,  aside  from  the  80  per  cent,  of  formaldehyde,  were 
formed.  Plating  the  platinum  anode  with  platinum  decreased 
the  yield  of  formaldehyde  at  the  expense  of  the  carbon  dioxide. 
With  an  anode  of  lead  peroxide  the  carbon  dioxide  exceeded 
the  aldehyde. 

Dony-Henault,3  by  measuring  the  depolarizing  action  of 
the  alcohol  in  3  n-sulphuric  acid,  found  no  indications  of  the 


1  Jahn,  Grundriss  d.  Elektrochemie  291  (1894). 
2Ztschr.  f.  Elektrochemie  6,  604  (1900). 
8  Ibid.,  533  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  59 

production  of  formaldehyde,  and  also  obtained  a  negative 
result  in  an  experiment. 

The  significance  of  all  the  conditions,  for  instance  the  acid 
concentration,  plainly  follows  from  the  different  results  of  the 
last-named  investigators. 

Ethyl  Alcohol. — In  the  case  of  this  alcohol  the  more  impor- 
tant results  have  been  obtained  by  the  investigators  above 
mentioned.  Schonbein l  and  Becquerel,2  and  Bartoli  and  Papa- 
sogli 3  also  later  carried  out  some  investigations  on  the  same 
subject.  The  results  of  the  researches  are,  in  general,  that  the 
final  products  formed  are  the  following: 

1.  In    sulphuric    acid    solution:     Aldehyde,    acetic    ester, 

formic  ester,  ethylidene   oxyethyl   ether  (CH3 — CH<^Qp  -^  j 

(Renard),  and  ethyl-sulphuric  acid. 

2.  Almeida  and  Deherain  state  that  in  the  electrolysis  of 
a  nitric-acid  solution  they  observed,  in  addition  to  these  oxida- 
tion  products,   carbonaceous  derivatives  of  ammonia  at  the 
negative  pole. 

3.  In  hydrochloric-acid  solution  4  chlor-acetic  acids  occur, 
in  addition  to  the  corresponding  oxidation  products  (Riche  5) . 

Habermann,  on  electrolyzing  the  alcohol  in  alkaline  solution, 
obtained,  besides  carbon  dioxide,  an  aldehyde  resin  (Ludersdorf 
and  Connel  6)  from  which  he  isolated  a  body  closely  related 
to  cinnamic  aldehyde.  In  aqueous  solution,  on  the  addition 
of  potassium  acetate,  the  alcohol  was  split  up  into  ethane, 
potassium  ethyl-carbonate,  carbon  dioxide,  and  acetic  ester. 

Jaillard7  and  Riche8  proved  the  formation  of  aldehyde  in 
sulphuric-  and  acetic-acid  solution.  In  hydrochloric-acid  solu- 

1  Tommasi,  Traite  d'Electrochimie  726  (1889). 

2Compt.  rend.  81,  1002  (1875)  et  al.  places  of  Compt  rend.;  Tommasi,, 
Traite1  d'Electrochimie  726  (1889) 

3  Wiedem.  Beiblatter  7,  121  (1882). 

4Pogg.  Ann.  19,77  (1830). 

5  Tommasi,  Trait£  d'Electrochimie  728  (1889). 

8  Pogg.  Ann.  36,  487;    Phil.  Mag    18,  47. 

7  Compt.  rend.  58,  203  (1864). 

8  Tommasi,  Traite"  d'Electrochimie  728  (1889), 


60  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

tion  Liidersdorf1  obtained  ester  like  compounds  containing 
chlorine.  Dony-Henault2  and  Elbs  and  Brunner3  have  shown 
how  to  obtain  certain  products,  depending  upon  definite  con- 
ditions. While  the  former  directed  his  aim  to  the  anode 
potential,  the  latter  sought  to  determine  precisely  the  chemical 
factors  which  influence  the  reaction. 

Dony-Henault  observed  that  alcohol  is  oxidized  in  sulphuric- 
acid  solution  already  at  an  anode  potential  of  1.3  volts,  as 
measured  in  connection  with  the  hydrogen  electrode.  The 
oxidation  of  acetaldehyde,  on  the  contrary,  requires  a  potential 
of  1.66  volts  to  convert  the  aldehyde  into  acetic  acid.  Hence, 
the  alcohol  can  be  oxidized  only  to  aldehyde  between  1.3  and 
1.66  volts.  The  experiment  proved  that,  when  a  platinized 
platinum  electrode  is  employed,  only  acetaldehyde  is  formed, 
and  this  quantitatively.  The  aldehyde  yield  decreases  at 
a  higher  potential,  the  acid  content  of  the  electrolytes  in- 
creases, and,  at  the  same  time,  ethyl-sulphuric  acid  can  be 
detected,  as  already  shown  by  Renard.  Dony-Henault  ascribes 
the  formation  of  this  acid  to  the  discharge  of  the  SCMons. 
According  to  Elbs,  a  purely  chemical  action  of  the  sulphuric 
acid  (which  becomes  concentrated  at  the  anode)  on  the  alcohol 
is  the  more  probable. 

Elbs  and  Brunner  electrolyzed  an  aqueous  solution  con- 
taining 5  g.-molecule  equivalents  of  alcohol  and  0.5-1  g.-mole- 
cule  equivalent  of  sulphuric  acid.  They  obtained  acetalde- 
hyde, acetic  acid,  and  carbon  dioxide,  but  no  carbon  monoxide. 
Acetic  acid  is  the  principal  product  at  a  bright  (polished)  plati- 
num electrode.  It  is  formed  with  a  current  yield  of  over  80%, 
the  yield  of  aldehyde  amounting  to  about  only  one  twentieth 
of  the  weight  of  the  acetic  acid. 

lodoform  from  Ethyl  Alcohol. — Chloroform  and  bromoform 
cannot  be  prepared  electrolytically  from  alcohol  (Elbs  and 
Herz4).  This  is  contrary  to  the  claims  of  the  D.  R.  P.  No. 

1  Pogg.  Ann.  19,  77  (1830). 

2  Ztschr  f.  Elektrochemie  6,  533  (1900). 

3  Ibid  6,604  (1900) 

4  Ibid.  4,  118  (1897). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  61 

29771  (1884).  Coughlin  l  has  substantially  verified  the  results 
of  Elbs  in  the  case  of  bromoform.  He  obtained  only  small 
quantities  of  this  body  which  can  be  easily  prepared  electro- 
lytically  from  acetone.  The  formation  of  iodoform,  on  the 
contrary,  takes  place  smoothly.  It  is  obtained  technically 
according  to  the  above-mentioned  patent.  Elbs  and  Herz 
have  established  the  following  conditions  for  this  reaction. 
The  course  of  the  reaction  is  illustrated  by  the  equation: 


The  electrolysis  is  best  performed  as  follows:  A  solution  of 
13-15  g.  calcined  soda  and  10  g.  potassium  iodide  in  100  cc. 
water  and  20  cc.  alcohol  is  placed  in  a  porous  earthenware 
cylinder  with  platinum  anode.  The  cathode,  of  nickel,  is 
surrounded  by  a  strong  solution  of  sodium  hydroxide.  The  elec- 
trolysis is  carried  out  at  a  temperature  of  70°  C.,  with  a  current 
density  at  the  anode  of  1  amp.  per  100  sq.  cm.,  and  is  continued 
for  2-3  hours.  After  several  hours  the  iodoform  crystallizes 
out,  the  current  yield  being  from  60-70  per  cent.  The  chief 
by-product  remaining  in  the  mother  liquor  is  sodium  iodate. 

The  reduction  of  the  iodoform  by  the  electrolytically  gener- 
ated hydrogen  is  insignificant,  according  to  the  observations 
of  Forster  and  Mewes.2 

This  behavior  permits  the  discarding  of  the  earthenware 
cylinder.  It  suffices  to  envelop  the  cathodes  with  parchment 
paper,  whereby  the  resistance  and  the  consumption  of  electrical 
energy  is  considerably  diminished.  The  diffusion  of  the  free 
alkali  hydroxide  away  from  the  cathode  necessitates  the  continu- 
ous introduction  of  carbonic-acid  gas,  because  caustic  alkali  pre- 
vents the  formation  of  iodoform,  while  carbonate  promotes  it. 
\Vhen  using  the  covered  cathodes,  20  g.  calcined  soda,  20  g. 
potassium  iodide,  and  50  cc.  alcohol  in  200  cc.  water  are 
electrolyzed  at  a  temperature  of  50°-70°,  a  current  of  carbonic- 
acid  gas  being  conducted  into  the  solution  between  anode  and 

1  Am.  Chem.  Journ.  27,  63  (1901). 

2  Ztschr.  f.  Elektrochemie  4,  268  (1897). 


62  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

cathode.  The  current  density  at  the  platinum  anode  can  be 
from  1  to  3  amp.,  at  the  platinum  cathode  4  to  8  amp.,  for 
100  sq.  cm.1  The  current  yield  is  about  80%.  A  series  of 
secondary  reactions,  which  are  not  mentioned  in  the  above 
equation,  occur  in  this  process.  The  hydriodic  acid  reacts  with 
the  soda,  liberating  carbonic  acid  and  forming  sodium  iodide, 
which  in  turn  is  subject  to  decomposition.  The  iodine  is  con- 
verted at  the  anode  into  hypoiodite  which  converts  the  alcohol 
by  oxidation  and  substitution  into  iodoform.  Alkali-iodate  is 
also  formed  by  oxidation  of  the  hypoiodite. 

The  reaction  is  the  same  as  that  involved  in  the  usual 
chemical  preparation  of  iodoform,  whereby  a  colorless  solution 
of  hypoiodite  (obtained  by  dissolving  iodine  in  a  sufficient 
quantity  of  potassium-hydroxide  solution)  is  made  to  react  with 
alcohol.  The  decomposition  potential  of  potassium  iodide, 
investigated  by  Dony-Henault,2  shows  that  the  iodine  as  such 
does  not  act  on  the  alcohol,  but  only  after  its  conversion 
into  hypoiodite.  The  iodine  ions  are  set  free  at  the  same 
anode  potential  no  matter  if  alcohol  is  added  or  not.  The 
alcohol  does  not  act  as  a  depolarizer  towards  the  iodine  ion; 
the  electrical  iodoform  synthesis  is  a  typical  secondary 
process. 

Preparation  of  Chloral. — Chloral  is  obtained  according  to  a 
process  3  devised  by  the  Chemische  Fabrik  auf  Aktien  (vorm.  E. 
Schering),  if  alcohol  is  permitted  to  flow  into  the  anode  chamber 
of  the  cell  during  the  electrolysis  of  a  potassium-chloride  solu- 
tion. Glucose,  starch,  and  sugar  thus  also  yield  chloral. 

Incidentally  it  may  also  be  mentioned  that  Sand  and 
.Singer  4  have  prepared  alcohols  electrolytically  by  reducing  the 
mercuric-iodide  compounds  of  alcohols.  The  cathode  is  a 
large  sheet  of  platinum  which  is  immersed  in  the  solution  of 

1  Elbs,  Ubungsbeispiele  fur   die  elektrolytische   Darstellung   chemischer 
Praparate  (Halle,  1902),  95. 

2  Ztschr.  f.  Elektrochemie  7,  57  (1900). 
»  Elektrochem.  Ztschr.  1,  70  (1894). 

<Ber.  d.  deutsch.  chem.  Gesellsch.  35,3179  (1902). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  63 

the  iodide  in  a  10%  potassium-hydroxide  solution: 
IHgCH2-CH2OH-f  2  H  =  Hg  +  HI+C2H5OH. 

Propyl  Alcohol.  —  n-Propyl  alcohol  offers  a  considerably 
greater  resistance  to  electrical  oxidation  than  methyl  or  ethyl 
alcohol,  according  to  experiments  made  by  Elbs  and  Brunner.1 
Propionic  acid  is  formed  as  the  principal  product,  with  a  cur- 
rent yield  of  over  90%,  at  bright  (polished)  and  platinized 
platinum  anodes,  as  well  as  at  lead  peroxide  anodes  when  the 
alcohol  is  electrolyzed  in  sulphuric-acid  solution.  A  little  pro- 
pionic  aldehyde  also  occurs  at  lower  current  densities.  The 
formation  of  carbon  mon-  and  dioxides  is  likewise  very  insig- 
nificant. 

Isopropyl  Alcohol,  under  conditions  similar  to  the  above 
electrolysis  of  n-propyl  alcohol,  decomposes  in  accordance  with 
the  equations: 

I.  CH3CH(OH)CH3+0=CH3COCH^  +  H20; 
II.  GH3COCH3  +  30  =CH3COOH  +HCOOH; 
III.  HCOOH  +  0=C02 


Acetone,  acetic  acid,  formic  acid,  and  carbonic  acid  are  formed. 
The  oxidation  takes  place  more  easily  than  in  the  case  of  the 
primary  alcohols,  and  yields  up  to  70%  acetone,  which,  however, 
is  readily  oxidized  further.  In  alkaline  electrolytes  the  alcohols 
are  converted  at  the  anode  into  complicated  condensation 
products  of  the  aldehydes. 

Isoamyl  Alcohol.  -  -  The  amyl  alcohol  produced  during 
fermentation  was  likewise  exposed  by  Elbs  and  Brunner  to 
the  anodic  current  action  in  sulphuric-acid  solution.  It  is 
converted  into  isovaleric  acid  with  a  current  yield  of  about 
80%.  Some  carbonic  acid  also  formed,  but  isovaleric  aldehyde 
was  not  present  under  the  chosen  conditions. 

Glycol.  —  Of  diatomic  alcohols  only  glycol  seems  to  have 
been  the  subject  of  investigation.  Renard2  observed  in  the 

1  Ztschr.  f.  Elektrochemie  6,  608  (1900). 

2  Ann.  chim.  phys.  [5]  17,  303,  313  (1879);   Compt.  rend.  81,  188  (1875), 
82,  562  (187C). 


64  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

electrolysis  of  a  sulphuric-acid  solution  of  glycol,  besides  the 
formation  of  hydrogen,  carbon  mon-  and  dioxide,  and  oxygen, 
that  trioxymethylene,  glycolic  acid,  formic  acid,  and  a  sub- 
stance isomeric  with  glucose  were  present  in  the  solution. 

In  phosphoric-acid  solution  the  results  are  similar. 

Glycerin. — Renard 1  also  investigated  tlie  behavior  of  glycerin. 
In  the  electrolysis  of  a  dilute  sulphuric-acid  solution  he  obtained 
besides  the  gases,  hydrogen,  oxygen,  carbon  monoxide  and 
dioxide, — trioxymethylene,  formic  acid,  acetic  acid,  gly eerie 
aldehyde,  and  a  body  to  whose  barium  compound  he  gave  the 
formula  (CsHaO^Ba  (gly eerie  acid?).  Further  electrolysis  of 
glyceric  aldehyde  gave  the  ordinary  oxidation  products,  and, 
as  in  the  case  of  glycol,  a  substance  closely  related  to  ordinary 
glucose.  Stone  and  McCoy2  found  similar  results  in  acid 
solution. 

Bartoli  and  Papasogli 3  repeated  these  experiments,  varying 
the  material  of  the  electrodes,  and  obtained  the  following 
results : 

Carbon  anode  and  platinum  cathode  gave  trioxymethylene, 
formic  acid,  glyceric  acid,  a  substance  similar  to  glucose,  and  a 
resin. 

Graphite  and  platinum  electrodes  yielded  the  same  products, 
but  a  larger  per  cent  of  formic  acid  was  formed  on  using  the 
latter.  Mellogen  was  formed  at  the  positive  electrode. 

Experiments  on  the  electrolysis  of  glycerin  in  alkaline  solu- 
tion were  made  by  Werther,4  Renard,5  Voigt,6  and  Stone  and 
McCoy.7  As  principal  products  there  resulted  acrolein  and 
acrylic  acid,  besides  glyceric  aldehyde  or  its  condensation 
products,  and  glyceric  acid,  graphitic  acid,  formic  acid  and, 
according  to  Voigt,  also  propionic  acid. 

1  Compt.  rend.  81,  188  (1875),  82,  562  (1876). 

2  Amer.  Chem.  Journ.  15,  656  (1893). 
8  Gazz.  chim.  13,  287  (1883). 

4  Journ.  prakt.  Chem.  88,  151  (1863). 
6  Compt.  rend.  82,  562  (1876). 

6  Ztschr.  f.  angew.  Chemie  107  (1894). 

7  Amer.  Chem.  Journ.  15,  656  (1893). 


ELECTROLYSIS   OF  ALIPHATIC  COMPOUNDS.  65 

Mannite. — This  hexatomic  alcohol  has  been  investigated 
by  Renard.1  Bizzarini  and  Campani2  have  published  the  re- 
sults of  an  investigation  on  erythrite. 

In  the  electrolyzed  fluid  from  mannite  Renard  obtained 
formic  acid,  trioxymethylene,  oxalic  acid,  a  sugar  isomeric  with 
glucose,  and  an  acid,  C6H808,  which  he  regarded  as  the  aldehyde 
of  saccharic  acid.  He  could  not  detect  mannonic  acid. 
Erythrite  is  oxidized  to  a  great  extent. 

4.  DERIVATIVES  OF  THE  ALCOHOLS. 

Mercaptans.  —  Bunge 3  electrolyzed  the  alkali  salts  of 
ethyl  and  methyl  mercaptans  and  observed  the  formation 
of  disulphides  at  the  positive  pole.  In  the  case  of  the  sulpho- 
compounds,  however,  the  free  acids  were  generated. 

Methyl-Sulphuric  Acid. — This  acid,  investigated  by  Renard,4 
yielded  hydrogen  at  the  negative  pole,  while  formic  acid,  carbon 
dioxide,  carbon  monoxide,  and  trioxymethylene,  besides  free 
sulphuric  acid,  were  found  at  the  positive  pole. 

Potassium  Trichlormethyl-Sulphate. — This  compound,  elec- 
trolyzed by  Bunge,5  gave  hydrogen  and  alkali  at  the  negative 
pole;  and  at  the  positive  pole  oxygen,  carbonic-acid  gas, 
chlorine,  sulphuric  acid,  and  perchloric  acid. 

Potassium  Trichlormethylsulphonate. — This  salt  was  elec- 
trolyzed by  Kolbe  6  in  neutral  concentrated  aqueous  solution 
and  gave  the  following  results: 

The  solution  became  strongly  acid  and  contained  free  hydro- 
chloric and  sulphuric  acids.  Hydrogen  was  gradually  evolved 
at  the  negative  pole.  After  the  decomposition  was  complete 
the  solution  contained  potassium  perchlorate,  which  was  also 
observed  in  the  case  of  potassium  trichlormethyl-sulphate. 

1  Ann.  chim.  phys.  [5]  17,  289,  316  (1879). 

2  Gazz.  chim.  13,  490  (1883). 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  3,  295,  911  (1870). 

4  Ann.  chim.  phys.  [5]  17,  289  (1879). 

6  Ber.  d.  deutsch.  chem.  Gesellsch.  3,  911  (1870). 
8  Journ.  prakt.  Chem.  62,  311  (1854). 


66  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Ethyl-Sulphuric  Acid. — Ethyl-sulphuric  acid,  on  being  sub- 
jected to  electrolysis  gave,  according  to  Renard,1  at  the  negative 
pole  hydrogen,  and  at  the  positive  pole  acetic  acid,  some  formic 
acid,  aldehyde,  and  sulphuric  acid.  In  concentrated  solution  a 
greater  proportion  of  acetic  acid  was  formed.  The  potassium 
salt  on  electrolysis  breaks'  up,  according  to  Hittorf,2  into  the 
ions  K-  and  -OS02-OC2H5. 

By  using  a  diaphragm,  Guthrie  3  obtained  aldehyde  and 
carbonic  acid  at  the  anode. 

Ethyl-Phosphoric  Acid  yielded  Renard 1  carbonic  acid, 
aldehyde,  and  free  phosphoric  acid. 

Potassium  Isoamyl-Sulphate,  according  to  Guthrie,3  is  de- 
composed into  oxygen,  valeric  acid,  and  sulphuric  acid,  while 

Potassium  Isoamyl-Phosphate  is  split  up  into  valeric  acid 
and  phosphoric  acid. 

Potassium  Isethionate  breaks  up  (Bunge  4)  into  hydrogen 
and  free  acid. 


5.  ALDEHYDES,  KETONES,  AND  THEIR  DERIVATIVES. 
(a)  Aldehydes. 

Aldehydes  occur  as  oxidation  products  of  primary  alcohols. 
They  are  readily  converted  into  acids  and  give,  when  reduced, 
primary  alcohols.  The  ketones,  the  oxidation  products  of 
secondary  alcohols,  are  oxidized  with  difficulty.  They  can 
only  be  converted  into  acids  by  simultaneously  splitting  up 
the  carbon  chain.  On  being  reduced  they  are  again  converted 
into  secondary  alcohols.  This  behavior  is  also  apparent  upon 
electrolysis;  however,  the  reaction  becomes  more  complicated 
as  the  molecule  becomes  more  complex  by  an  enlargement  of 
the  carbon  chain  and  the  entrance  of  substituents.  Extensive 
decompositions  then  occur  readily  and  the  decomposition  prod- 


1  Ann.  chim.  phys.  [5]  17,  289  (1879). 

2  Pogg.  Ann.  106,  530  (1859). 
8  Lieb.  Ann.  99,  64  (1856). 

4Ber.  d.  deutsch   chem.  Gesellsch.  3,  911  (1870). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  67 

ucts,  which  are,  naturally,  often  neither  aldehydes  or  ketones,  are 
changed  further  in  accordance  with  their  individual  nature. 
Aldehydes  and  ketones  (like  the  alcohols)  are  non-electrolytes, 
and  act  merely  as  depolarizers.  The  acids,  however,  which 
are  formed  by  the  reaction,  often  play  a  decisive  part  in  the 
current  conductivity,  so  that  more  thorough  experiments  are 
required  in  many  cases  to  fully  learn  the  conditions  electrically 
dominating. 

The  fact  that  aldehydes  occur  among  the  reaction  products 
of  the  alcohol  electrolyses  is  perhaps  the  reason  why  they  have 
rarely  been  chosen  as  the  starting-point  in  special  experiments. 
Considering  the  important  role  the  aldehydes  play  as  intermedi- 
ate members  of  syntheses,  the  treatment  of  this  subject  would 
be  highly  remunerative,  particularly  "with  the  aid  of  potential 
adjustments  at  certain  values.  More  attention  has  recently 
been  given  to  work  on  the  ketones. 

Derivatives  of  Formaldehyde  and  Acetaldehyde. — According 
to  Tafel  and  Pfeffermann,1-  the  phenylhydrazones  of  aldehydes 
are  readily  converted  into  a'mines  by  reduction  in  sulphuric- 
acid  solution  at  a  lead  cathode.  Thus  ethylidene  phenyl- 
hydrazine  yields  about  60%  of  the  theoretical  percentage  of 
pure  ethylamine  salt.  The  decomposition  of  glyoxime  is  more 
complicated.  Besides  ammonia  and  glyoxal  and  a  small 
quantity  of  an  acid  (glyoxylic  acid  ?)  there  is  formed  as  the 
principal  product  the  crystalline  sulphate  of  a  base,  C2Hg02N2, 
the  nature  of  which  could  not  be  determined  with  certainty. 
Ethylenediamine  is  not  formed.  Nor  was  a  diamine  obtained 
from  methylglyoxime. 

The  condensation  products  of  aldehydes  with  ammonia  or 
amido-compounds  are  easily  reduced  to  amines  in  sulphuric-acid 
solution  at  lead  cathodes.  Thus  hexamethylenetetramine  yields 
methylamine  (Knudson  2);  ethylideneimine,  ethylamine;  the  base 
from  acet aldehyde  and  ethylamine,  diethylamine.  Aromatic 
aldehydes  behave  similarly.  The  Farbwerke-  vorm.  Meister, 

1  Ber.  d.  deutsch.  Gesellsch.  35, 1510  (1902). 
2D.  R.  P.  No.  143197  (1902). 


68  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Lucius  and  Br  lining  1  obtain  the  same  effect  in  neutral  or  am- 
moniacal  solution  of  the  condensation  products  of  fatty  alde- 
hydes with  ammonia. 

Chloral  Hydrate. — Tommasi  2  electrolyzed  a  sulphuric-acid 

solution  of  chloral  hydrate  and  was  able  to  detect  the  presence 

of  hydrochloric  acid.     On  using  diaphragms  an  abundance  of 

chlorine  was  evolved  at  the  anode,  and  acetalhedyde  collected 

at  the  cathode. 

Grape  Sugar. — This  sugar  (investigated  by  Renard 3)  on 
being  subjected  to  the  action  of  the  current  broke  up  into 
carbon  mon-  and  dioxide,  formic  acid,  trioxymethylene,  and 
saccharic  acid.  O'Brien  Gunn 4  mentions  that  the  aqueous 
glucose  solution  is  converted  by  cathode  reduction  into  mannite : 

C6H1206  +  2H=C6H1406. 

Cane  Sugar. — On  electrolyzing  a  concentrated  solution  of 
cane  sugar,  Brester 5  found  that  the  solution  turns  strongly 
acid  and  acquires  reducing  properties,  very  little  carbon  di- 
oxide being  evolved.  He  was  unable  to  determine  the  nature 
of  the  substance  which  he  isolated  by  distillation,  and  which 
was  free  from  formic  and  acetic  acids.  Continued  electrolysis 
produced  further  oxidation. 

The  same  author  made  some  experiments  on  the  electrolysis 
of  dextrine,  gum  arabic,  and  collodion,  but  obtained  no  note- 
worthy results. 

The  general  impression '-gained  from  these  investigations  is 
one  of  successive  oxidation.  The  electrolytic  oxygen  gradually 
oxidizes  the  substances,  the  final  product  being  carbon  dioxide. 
Intermediate  products  are  formed  during  the  electrolysis,  their 
quantity  varying  with  the  duration  of  the  electrolysis.  In  fol- 
lowing out  these  processes  it  is  of  especial  importance  imme- 
diately to  withdraw  the  electrolyzed  liquid  from  the  action 

1  D.  R.  P.  No.  148054  (1903). 

2  Tommasi,  TraitS  d'Electrochimie  741  (1889). 

3  Ann.  chim.  phys.  [5]  17,  289  (1879). 

4  D.  R.  P.  No.  140318  (1900). 

5  Bull.  soc.  chim.  8,  23  (1866). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  69 

I 

of  the  current,  in  the  manner  practiced  by  Miller  and  Hofer,1 
by  allowing  the  solution  to  flow  slowly  over  the  electrodes. 
Experiments  of  this  nature  have  not  yet  been  made  here. 

Ulsch2  has  made  some  observations  on  the  complete  elec- 
trochemical oxidation  of  cane  sugar  to  carbonic,  acid  and  water. 
In  a  sulphuric  acid  of  1.15  sp.  gr.,  with  the  addition  of  manganese 
sulphate  as  an  oxygen-carrier,  about  98%  of  the  theoretically 
calculated  amount  of  carbonic  acid  is  obtained.  The  oxidation 
at  40°-80°  in  barium-hydrate  solution  is  also  fairly  complete, 
but  not  directly  to  carbonic  acid;  oxalate  appears  also  to  be 
formed. 

The  apparently  successful  attempts  at  electrical  purification 
of  sugar  juice,  for  which  a  large  number  of  patents  3  have  been 
taken  out,  may  be  briefly  mentioned  here.  The  gist  of  the 
various  methods  lies,  on  the  one  hand,  in  the  destruction  of 
the  impurities  by  oxidation  at  the  anode,  and,  on  the  other 
hand,  in  the  production  of  precipitates  which  carry  down 
colored  organic  substances  and  facilitate  crystallization  of  the 
sugar  by  eliminating  these  impurities/ 

b.  Ketones. 

Acetone. — Friedel,4  by  electrolyzing  a  sulphuric-acid  solu- 
tion of  acetone,  obtained  carbonic  acid,  acetic  acid,  and  formic 
acid.  Mulder 5  and  Riche 6  were  able  to  isolate  mono-  and 
dichloracetone  from  the  hydrochloric-acid  electrolyte,  and 
monobromacetone  from  a  hydrobromic-acid  solution.. 

These  older  investigations  are  supplemented  by  more  recent 
researches  with  more  exact  results. 

According  to  a  process  patented  by  E.  Merck,7  acetone  is 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  461  (1894). 

2  Ztschr.  f.  Elektrochemie  5,  539  (1899). 

3  Ibid.    1,   251    (1894),   3,   16   (1896);    Jahrb.    d.    Elektrochemie  3,   322 
(1896),  8,  628  (1901). 

4Lieb.  Ann.  112,  376  (1859). 
5  Jahresb.  JF.  Chemie  339  (1859). 
c  Compt.  rend.  49,  176  (1859). 
7D.  R.  P.  No.  113719  (1899). 


70  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

reduced  in  acid  and  alkaline  solution  at  a  lead  cathode  to 
isopropyl  alcohol  and  pinacone.  The  yields  of  the  latter, 
however,  are  better  in  acid  solution.  About  40  parts  of 
isopropyl  alcohol  and  20  parts  of  pinacone  are  obtained  from 
100  parts  of  acetone,  if  a  sulphuric-acid  electrolyte  is  employed. 
The  reactions  take  place  according  to  the  equations: 

1.  CH3COCH3+2H=CH8CH(OH)CH3, 

2.  2CH3COCH3  +2H  =CH3C(OH)CH3 

CH3C(OH)CH3. 

The  claims  of  the  patent  were  verified  by  Elbs.1  Elbs  and 
Brand  2  publish  the  following  details :  In  a  10%  sodium-hydrox- 
ide solution  the  reduction  of  acetone  at  a  lead  cathode  proceeds 
even  with  a  low  current  density,  hydrogen  being  continually 
liberated.  The  yield  of  isopropyl  alcohol  and  pinacone  is 
small;  and  the  by-products  are  mesityloxide,  phorone,  and 
other  condensation  products.  About  120  g.  pure  isopropyl 
alcohol  and  60  g.  pinacone  hydrate  were  obtained  in  dilute 
sulphuric-acid  solution  from  300  g.  acetone,  lead  cathodes 
being"  also  used  in  this  case.  At  mercury  cathodes  the  reduc- 
tion of  acetone  leads  to  a  smooth  conversion  into  isopropyl 
alcohol  (Tafel3),  without  appreciable  quantities  of  pinacone 
being  formed.  The  cathode  electrolyte  was  40%  sulphuric 
acid.  The  experiments  were  made  by  keeping  the  solution 
cool  with  ice. 

Richard  4  reverts  to  the  attempts  of  Mulder  and  Riche  to 
prepare  halogen  compounds  of  acetone.  These  substitution 
processes  occur,  of  course,  at  the  anode.  With  a  low  anode 
current  density  and  in  concentrated  hydrochloric-acid  solution 
(3  vol.  acetone  to  2  vol.  hydrochloric  acid)  monochloracetone 
is  produced,  the  fluid  being  ice-cooled,  and  unattackable  elec- 

^tschr.  f.  Elektrochemie  7,  644  (1901).  See  also  Elbs  and  Schmitz, 
Journ.  f.  prakt.  Chem.  51,  591  (1895). 

2  Ztschr.  f.  Elektrochemie  8,  783  (1902). 

8  Ibid.,  288  (1902). 

4Compt.  rend.  133,  878  (1901). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  71 

trodes  without  diaphragms  employed.  Monobromacetone  is 
obtained  in  a  similar  manner,  but  a  diaphragm  and  a  some- 
what higher  temperature  (35°-40°)  are  advantageous  in  its 
preparation. 

Chloroform. — Teeple  l  has  verified  the  claims  of  Schering's 2 
patent  as  to  the  preparation  of  chloroform  from  acetone.  The 
solution  of  the  problem  consisted  simply  in  electrolyzing  a 
solution  of  a  chloride  in  the  presence  of  acetone  under  condi- 
tions that  would  continuously  give  the  greatest  possible  yield 
of  hypochlorite.  The  most  important  conditions  for  this 
purpose  are  a  temperature  below  25°,  a  solution  containing 
no  alkali,  or  as  little  as  possible,  a  high  current  density  at  the 
cathode,  and  a  comparatively  low  one  at  the  anode  (Oettel, 
Forster,  etc).  Teeple  gives  the  following  details:  In  an 
ordinary  cylinder  of  150-200  cc.  capacity  place  100  cc.  water, 
20  g.  sodium  chloride,  and  4  cc.  acetone;  a  platinum  cylinder 
serves  as  anode,  and  a  platinum  wire  as  cathode;  close  the 
vessel  with  a  cork  connected  with  a  reflux  condenser;  cool  the 
apparatus  with  running  water  and  electrolyze,  passing  in  a  slow 
stream  of  chlorine  as  needed  to  neutralize  the  alkali;  anode 
current  density  about  6  amp.  per  sq.  dm.  or  less.  After  8 
to  10  hours  a  layer  of  chloroform  may  be  removed  from  the 
bottom  of  the  electrolyte. 

The  electrolysis  of  a  calcium-chloride  solution  in  the  presence 
of  acetone  would  be  the  best  method  of  forming  chloroform 
if  the  high  resistance  due  to  the  deposits  forming  on  the  cathode 
could  be  overcome  in  some  way. 

Bromoform. — As  already  mentioned,  bromoform  is  not  formed 
from  alcohol  under  the  conditions  which  are  suitable  for  the 
preparation  of  iodoform.  It  is  possible,  however,  to  convert 
acetone  quantitatively  into  bromoform  (Coughlin3),  if  acetone 
and  potassium  bromide  are  subjected  in  aqueous  solution  at- 
25°  to  the  anodic  current  action  and  soda  is  gradually  added. 
A  diaphragm  is  used.  More  thorough  experiments  on  this 

1  Journ.  Amer.  Chem.  Soc.  26,  536  (1904). 

2D.  R.  P.  29771  (1884). 

8  Am.  Chem.  Journ.  27,  63  (1902). 


72  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

method  were  carried  out  by  Miiller  and  Loebe.1  They  showed 
that  the  diaphragm  becomes  unnecessary  if  a  strong  current 
of  carbonic-acid  gas  is  passed  through  the  electrolytes  kept  at 
15°-17°.  They  thus  obtained  a  current  yield  of  90.2%  bromo- 
form.  With  a  lower  yield,  oxidation  and  further  bromination 
occurs  besides  the  formation  of  bromoform.  This  latter  takes 
place  in  stoichiometrical  proportions  according  to  the  equation 

CH3COCH3  +6Br +H20  =CHBr3  +CH3COOH +3HBr, 
or  in  the  form  of  an  ionic  equation, 

3Br'  +60  +  H20  +CH3COCH3  =CHBr3  +CH3COOH  +  3H'. 

This  formula  is  not  intended  to  show  that  the  acetone  acts 
directly  as  a  depolarizer  of  the  bromine  ion.  The  reaction 
mechanism  has  not  yet  been  completely  elucidated, 

lodoform2  from  Acetone. — Teeple3  mentions  a  method  by 
which  almost  the  theoretical  yield  of  iodoform  can  be  obtained 
by  the  electrolysis  of  a  potassium-iodide  solution  in  the  presence 
of  acetone.  No  diaphragm  is  required,  the  essential  feature 
being  the  gradual  addition  of  a  substance  like  hydrochloric 
acid,  hydriodic  acid,  or,  better,  iodine,  to  neutralize  the  excess 
of  potassium  hydroxide  as  fast  as  it  is  formed.  The  tempera- 
ture is  kept  below  25°,  and  the  electrolyte  thoroughly  stirred; 
in  .fact  the  same  current  conditions  should  be  observed  as  in 
the  case  of  chloroform  above  mentioned,  the  aim  in  this  case 
also  being  to  maintain  the  conditions  always  favorable  for  the 
production  of  a  maximum  amount  of  hypoiodite. 

Oxidation  of  Ketoximes. — According  to  an  investigation 
made  by  J.  Schmidt,4  ketoximes,  on  electrolysis  in  dilute  sul- 
phuric-acid solution,  are  decomposed  in  such  a  way  that  pseudo- 
nitroles  are  formed  besides  other  nitroso-compounds.  If 
acetoxime  is  oxidized  at  a  temperature  not  over  10°  in  a  2% 

1  Ztschr.  f.  Elektrochemie  10,  409  (1904). 

2  See  also  p.  60. 

3  Journ.  Amer.  Chem.  Soc.  26,  170  (1904). 

4  Ber.  d.  deutsch.  chem.  Gesellsch.  33,  871  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  73 

sulphuric-acid  solution,  using  a  platinum  anode,  and  an  earthen- 
ware cell  as  diaphragm,  the  anode  fluid  is  soon  colored  blue; 
at  the  same  time  a  white  crystalline  substance  is  precipitated 
upon  the  anode.  This  substance  is  propylpseudonitrole, 

This   was   formed   perhaps   in   the   following 


manner : 

4(CH3)  2C :  NOH  +  3N204  =  4(CH3)  2<X^^  +  2H20  +  2NO. 

A  part  of  the  acetoxime  will  split  up  upon  electrolysis,  oxides 
of  nitrogen  being  given  off,  and  these  latter  in  the  nascent 
state  will  convert  any  unchanged  acetoxime  into  propylpseu- 
donitrole. A  blue  nitroso-compound  can  be  isolated  from  the 
anode  solution.  A  diaphragm  is  unnecessary  in  these  experi- 
ments. Diethylketoxime  and  methylethylketoxime  behave  just 
like  acetoxime. 

Isopropylamine  is  formed  in  the  reduction  of  acetoxime  in 
sulphuric-acid  solution  at  a  lead  cathode  (Tafel  and  Pfeffer- 
mann x).  This  process  is  a  general  one.  The  electrolytic 
reduction  of  ketoximes  leads,  like  that  of  the  aldoximes  and 
phenylhydrazones,  to  the  final  formation  of  amines.  About 
66%  of  the  theoretically  possible  quantity  of  isopropylamine 
is  formed  from  acetoxime;  acetonphenylhydrazone  gives  about 
the  same  yield. 

Glyoxime,  OHN  =  CH:CH:NOH,  under  similar  conditions, 
yields,  as  the  chief  product  (about  60%  yield)  a  substance 
whose  reactions  probably  characterize  it  as  /?-ethylenedihy- 
droxylamine : 

CHiNOH  CH2NHOH 

+  2H2  =    | 
:NOH  CH2NHOH. 

The  electrolyte  also  contains  ammonia,  glyoxal,  and  small 
quantities  of  acid  (glyoxalic  acid). 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  35,  1510  (1902) ;  see  also  D.  R.  P. 
No.  141346  (1902). 


74  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Isonitrosoacetone.  —  Ahrens  and  Meissner  1  electrolyzed 
isonitrosoacetone,  CH3COCHNOH,  in  sulphuric-acid  solution 
to  obtain  amidoacetone.  However,  a  poor  yield  of  dimethylpy- 
razine,  CeHsM2  (ketine)  was  obtained. 

Methylethylketone.  —  This  substance,  reduced  at  a  lead 
cathode  in  the  same  manner  as  acetone  by  Elbs  and  Brand,2 
gives  very  unfavorable  results  in  alkaline  solution.  In  sul- 
phuric-acid splution,  although  the  yield  is  insufficient,  there 
were  obtained  the  modification  of  methylethylpinacone  melting 

at  50°, 

/CH3 


>C(OH)-C(OH)<; 
C2H/  \C2H5, 

and  secondary  butyl  alcohol,  CH3CH(OH).CH2-CH3. 

Acetylacetone.  —  This  is  said  to  pass,  in  alcoholic  solution, 
into  tetracetylethane  (Mulliken  3)  : 

CH3-C(\  CHaCCX  /CO-CH3 

2  >CH2  =  >CH-CH<  +  H2. 

CH3-CCK  CHaCCK  XCO-CH3 

The  substance  therefore  breaks  up  into  H*  and  (CH3CO)2CH'; 
the  anions  unite  at  the  anode  to  the  resulting  compound. 

Acetylacetondioxime,  in  a  30%  sulphuric  acid  at  a  lead 
cathode,  is  converted  into  dimethylpyrazolidine  and  2.4-dia- 
minopentane  (Tafel  and  Pfeffermann  4). 

CH3  CH3  CH3 

i  i  i 

C:N-OH  CH-NH  CH-NH2 

I  I  I 

CH2  —  >     CH2  —  »     CH2  • 

i  i  i 

C:N-OH  CH-NH  CH-NH2 

I  I  I 

CH3  CH3  CH3 

Acetylacetonedioxime.      Dimethylpyrazolidine.      Diaminopentane. 

Pyrazolidine  is  the  chief  product. 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  30,  532  (1897). 

2  Ztschr.  f.  Elektrochemie  8,  786  (1902). 

3  Amer.  Chem.  Journ.  15,  323  (1893). 

4  Ber.  d.  deutsch.  chem.  Gesellsch.  36,  219  (1903). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  75 

6.  ACIDS. 

While  the  substances  thus  far  discussed  are  active  only  as 
depolarizers,  but  not  as  electrolytes,  the  conditions  are  different 
in  the  case  of  acids  and  their  salts.  These  are  primarily  elec- 
trolytes; their  ions  take  care  of  the  current  conductivity  and 
are  first  separated  or  brought  into  reaction  at  the  electrodes. 
In  general,  hydrogen  ions  are  discharged  at  the  cathode  when 
acids  form  the  electrolyte,  and  metal  ions  in  the  case  of  salts; 
acid-radical  ions  are  discharged  at  the  anode.  The  latter  have 
the  form  RCOO  and  are  subject  to  a  series  of  reaction  possi- 
bilities. By  reacting  with  water  the  acid  is  again  regenerated, 
oxygen  being  evolved' 

RCOO  +  H20  =  RCOOH  +  OH. 

Often,  however,  two  anions  unite,  carbon  dioxide  being  split  off: 


wherein,  if  R  is  a  hydrocarbon  radical,  like  methyl,  ethyl,  etc., 
hydrocarbons  are  formed  having  double  the  number  of  carbon 
atoms  contained  in  the  radicals  united  with  the  carboxyl 
group.  Thus  ethane  is  synthecized  from  acetic  acid.  This 
simple  form  of  reaction  is  often  not  the  predominating  one, 
which  will  be  explained  more  fully  under  the  separate  sub- 
stances. 

An  acid  can  often  develop  acid  properties  at  other  than  the 
carboxyl  groups,  e.g.  hydroxyl  and  methylene  groups.  In 
that  case  there  must  occur  the  corresponding  ions  which  are 
able  to  direct  the  reaction  in  entirely  different  channels  from 
those  mentioned.  Thus,  as  is  well  known,  the  methylene  group 
placed  between  two  carboxyl  or  ester  groups  is  capable  of 
forming  salts.  Such  salts  as,  for  instance,  sodium  diethyl- 
malonic  ester,  behave,  on  electrolysis,  in  a  manner  analo- 
gous to  that  of  the  salts  of  carboxylic  acids.  By  determining 
their  conductivities,  Ehrenfeld  1  has  recently  proved  that  the 
1  Ztschr.  f.  Elektrochemie  9,  335  (1903). 


76  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

methylene  groups  of  succinic  acid,  malonic  acid,  and  glutaric 
acid  are  capable  of  forming  hydrogen  ions. 

The  first  successful  experiments  in  the  electrolysis  of  ali- 
phatic car  boxy  lie  acids  were  made  by  Kolbe.1  These  experi- 
ments are  supplemented  by  the  researches  of  Kekule,2  Brown 
and  Walker,3  Mulliken,4  and  Weems,5  who  amplified  our  knowl- 
edge regarding  this  subject  which,  still  further  investigated 
in  the  most  varied  directions  by  a  number  of  investigators, 
has  yielded  valuable  results. 

Carbonic  Acid. — Carbonic  acid  deserves  mention  here  be- 
cause it  can  be  converted  electrolytically  into  formic  acid. 
Royer  6  observed  its  formation  at  zinc  and  zinc-amalgam  elec- 
trodes in  the  electrical  reduction  of  carbonic  acid  dissolved 
in  water,  a  current  of  the  gas  being  conducted  through  the  latter 
during  electrolysis.  Klobukow 7  was  likewise  able  to  prove 
the  presence  of  formic  acid  in  water  which  was  electrolyzed 
and  through  which  a  current  of  carbonic-acid  gas  was  passed. 

Lieben  8  has  made  extensive  experiments  on  the  reductivity 
of  carbonic  acid.  He  obtained  formic  acid  as  the  sole  reduction 
product  of  carbonic  acid.  The  supposition  of  Bach 9  that 
formaldehyde  must  also  be  formed  is  false.  The  formation 
of  formaldehyde  was  never  proved.  Quite  recently  Coehn 
and  Jahn 10  have  shown  that  formic  acid  is  the  only 
tangible  reduction  product.  They  succeeded  in  obtaining 
quantitative  current  yields,  using  carefully  prepared  amal- 
gated  zinc  electrodes,  as  already  previously  employed  by 
Royer,  and  using  a  cold  saturated  potassium-sulphate  solution 
as  electrolyte.  According  to  Constam  and  Hansen,11  potassium 

1  Lieb.  Ann.  69,  257  (1849),  113,  244  (1860). 

2  Ibid.  131,  79  (1864). 

3  Ibid.  261,  107  (1891),  274,  41  (1893). 
« Amer.  Chem.  Journ.  15,  523  (1893). 

6  Ibid.  16,569  (1894). 

6  Compt.  rend.  70,  731  (1870). 

7  Journ.  f.  prakt.  Chem.  [2]  34,  126  (1887). 
8Monatshefte  f.  Chem.  16,  211  (1895),  18,  582  (1897). 
9  Compt.  rend.  126,  479  (1898). 

l0Ber.  d.  deutsch.  chem.  Gesellsch.  37,  2836  (1904). 
11  Ztschr.  f.  Elektrochem.  3,  137  (1896),  3,  445  (1897). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  77 

percarbonate  is  formed  when  a  saturated  solution  of  potassium 
carbonate  is  electrolyzed  at  —10°  to  —15°,  particularly  at  a 
high  current  density,  the  anions  KCOs  uniting  when  set  free : 

KOX 

>CO 
(X 
2KC03  =  K2C206  =     I 


KO 


The  potassium  salt  is  precipitated  as  a  blue  powder.  It  has 
not  been  possible  to  isolate  other  salts  and  free  percarbonic 
acid.  The  experiments  of  Salzer,1  however,  indicate  that  the 
free  acid  may  occur  perhaps  intermediately.  He  proved  the 
presence  of  active  oxygen  in  a  solution  of  potassium  bicarbonate 
through  which  was  passed  a  continuous  current  of  carbonic- 
acid  gas. 

1.  MONOBASIC  ACIDS,  CnH2n02. 

Formic  Acid.  —  This  acid  and  its  salts  have  been  the  sub- 
jects of  thorough  electrolytic  investigations.  These  were 
carried  out  chiefly  by  Brester,2  Renard  3  and  Bourgoin,4  Bar- 
toli  and  Papasogli,5  Jahn,6  etc. 

The  progress  of  the  decomposition  is  accompanied  by  the 
evolution  of  carbon  dioxide  and  oxygen  at  the  positive  pole 
and  hydrogen  at  the  negative  pole.  The  quantitative  relations 
of  the  decomposition  products  vary  with  the  concentration  of 
the  solution  and  the  density  of  the  current.  The  reactions 
occur  according  to  the  following  equations* 

HCOOH  =  HCOO  +  H, 
2HCOO  +  H20  =  2HCOOH  +  0, 


1  Ztschr.  f.  Elektrochem.  8,  902  (1902). 

2  Ztschr.  f.  Chem.  60  (1866). 

3  Ann.  chim.  phys.  [5]  17,  289  (1878) 

4  Ibid.  [4]  14,  157  (1868). 
8Gazz.  chim.  13,  22,  28  (1883). 

•  Wied.  Ann.  (N.  F.)  37,  408  (1889). 


78  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

It  is  therefore  theoretically  impossible  to  effect  the  com- 
plete decomposition  of  the  formic  acid  present.  In  the  elec- 
trolysis of  sodium  formate,  carbon  dioxide  and  formic  acid 
are  in  fact  always  formed  at  the  positive  pole  and  hydrogen 
and  sodium  hydroxide  at  the  negative  pole. 

A  splitting  up  of  the  anions  HCOO  into  H  and  C02  at  the 
anode  does  not  occur,  since  the  oxidizing  hydroxyl  ions  split 
off  the  hydrogen  as  water  (Hofer  and  Moest  *).  The  discussion 
of  the  other  salts  is  unnecessary  since  their  behavior  is  quite 
analogous. 

The  dependence  of  the  decomposition  of  formic  acid  upon 
the  conditions  of  the  experiment  has  been  investigated  by 
Peter  sen  2  and  Salzer.3 

Petersen  found  that,  if  the  solution  was  concentrated,  the 
current  strength  exercised  only  a  trifling  influence  on  the 
decomposition  phenomena  in  the  electrolysis  of  sodium  formate. 
According  to  Salzer 's  researches,  formic  acid  in  sulphuric-acid 
solution  cannot  completely  suppress  the  evolution  of  oxygen 
at  a  platinized  anode.  Sodium  formate  is  for  the  most  part 
converted  into  carbonate;  in  neutral  solution  small  quantities 
of  per  carbonate  are  also  formed. 

Formic  ester  in  sulphuric-acid  solution  is  attacked  only 
with  difficulty  in  the  cathode  chamber  (Tafel  and  Friedrichs  4) ; 
acetic  ester,  cyanacetic  ester,  and  phenylacetic  ester,  it  may 
be  remarked  here,  are  not,  at  tacked  at  all. 

Acetic  Acids. 

Acetic  Acid. — Glacial  acetic  acid  is  a  poor  conductor  of  elec- 
tricity. According  to  Lapschin  and  Tichanowitsch,5  its  de- 
composition when  effected  by  900  Bunsen  elements  yields  at 
the  anode  carbon  mon-  and  dioxide,  and  at  the  cathode  carbon 


1  Lieb.  Ann.  323,  284  (1902). 

2  Ztschr.  f.  phys.  Chem.  33,  106  (1900). 

3  Ztschr.  f.  Elektrochemie  8,  893  (1902). 

4  Ber.  d.  deutsch.  chem.  Gesellsch.  37,  3187  (1904). 

5  Neue  Peters.  Acad.  Bull.  4,  81  (1861). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  79 

and  a  small  quantity  of  a  gas  the  nature  of  which  was  not 
established. 

Bourgoin,1  on  electrolyzing  the  dilute  acid,  observed  hydro- 
gen at  the  negative  pole  and  oxygen,  carbon  dioxide,  and  traces 
of  carbon  monoxide  at  the  positive  pole. 

The  reactions  involved  in  the  decomposition  of  the  alkali 
salts  are  more  interesting.  Kolbe,2  on  decomposing  a  concen- 
trated solution  of  potassium  acetate,  obtained  a  hydrocarbon 
in  addition  to  other  decomposition  products.  According  to 
the  idea  then  prevailing,  acetic  acid  underwent  oxidation  in 
the  sense  that  it  was  thereby  changed  into  carbon  dioxide 
and  methyl,  both  of  which  appeared  at  the  positive  pole,  while 
at  the  negative  pole  only  hydrogen  was  evolved,  and  a  part 
of  the  methyl  was  oxidized  to  methyl  oxide.  The  hydro- 
carbon evolved  was  in  fact  ethane,  which  always  accompanies 
the  decomposition  of  potassium-acetate  solutions,  while  the 
other  decomposition  products  formed  vary  with  the  density 
of  the  electric  current  and  the  temperature  of  the  solutions. 
Thus  Kolbe  identified  methyl  ether  and  methyl  acetate  in 
the  solution,  .while  Bourgoin  observed  no  decomposition  products 
other  than  carbon  monoxide  and  dioxide.  Jahn,3  who  em- 
ployed currents  of  very  low  electrode  density,  obtained  by  the 
electrolysis  of  an  almost  saturated  solution  of  sodium  acetate 
only  carbon  dioxide,  ethane,  and  hydrogen.  The  formation 
of  ethane  can  be  explained  by  assuming  either  the  direct  oxida- 
tion of  the  acetic  acid, 


or  the  decomposition  of  the  anion, 


»  Ann.  chim.  phys.  [4]  14,  157  (1868). 
2Lieb,  Ann.  69.279  (1849). 
Grundriss  d.  Elektrochemie  (1895),  292. 


80  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Kekule  1  advanced  a  theory  based  upon  the  phenomena  of 
decomposition,  and  from  this  deduced  certain  formulae  which 
make  it  possible  to  predict  the  nature  of  the  products  resulting 
from  the  electrolysis  of  monobasic  and  dibasic  acids  of  the 
fatty-acid  series.  Since,  however,  the  reaction  is  influenced 
by  the  slightest  variation  of  conditions,  his  formulae  hold  good 
only  in  the  case  of  the  decomposition  of  perfectly  pure  sub- 
stances, a  condition  seldom  met  with  in  practice. 

Lob2  is  in  favor  of  accepting  in  certain  cases  the  theory 
advanced  by  Kekule,  who  sought  by  experiments  to  prove  the 
intermediate  formation  of  the  anhydride,  while  Schall 3  assumes 
the  formation  of  an  acid  superoxide : 

R-COO 
2RCOO  = 

R-COO 
R-COO 

=  R-R+2C02. 
R-COO 

This  conclusion  is  drawn  from  the  observed  fact  that  the 
dithionic  acids,  on  the  electrolysis  of  their  alkali  salts,  actually 
give  acid  supersulphides  which  correspond  with  the  superoxides: 

R-CSS— +R-CSS-  =R-CSSv 

R-CSS/ 

In  contrast  to  the  acid  superoxides,  the  acid  supersulphides 
are  stable  compounds. 

Bourgoin  draws  the  following  conclusions  from  his  experi- 
ments :  He  considers  the  intermediate  anhydride  formation 
as  the  most  important  process  in  the  electrolysis  of  organic 
acids;  this  brings  about  the  secondary  oxidation  processes, 
oxygen  being  given  off.  He  also  considers  as  secondary  reac- 
tions, the  transition  from  the  acid  anhydride  to  the  hydrate 
with  the  taking  up  of  water,  and  the  oxidation  of  acids  by  the 
oxygen  derived  from  the  acid  itself.  This  explanation  agrees 

1  Lieb.  Ann.  131,  70  (1864). 

3  Ztschr.  f.  Electrochemie  3,  43  (1896). 

8  Ibid.  3,  83  (1896). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  81 

with  the  fact  that  water  is  a  weak  electrolyte  and  serves  prin- 
cipally as  a  dissociating  medium.    The  typical  processes  in 
the  electrolysis  of  acetic  acid  are  hence  the  following: 
Electrolytic  decomposition: 

/CH3CCX  \ 

2CH3COOK  =  (  >0  +  0    +  2K. 

\CH3CCK 

Characteristic  oxidation : 

CH3-C(X 

>0+0=2C02+C2H6. 
CHa-CCK 

Kolbe  and  Kampf,1  on  electrolyzing  a  concentrated  potassium- 
acetate  solution,  obtained  at  the  anode  acetic  methyl  ester, 
formic  methyl  ester,  ethane,  ethylene,  and  carbon  dioxide; 
and  at  the  cathode  hydrogen  and  potassium  hydroxide.  In 
an  alkaline  solution  of  the  salt  Bourgoin2  obtained,  amongst 
other  products,  sodium  formate  (by  reduction  of  the  carbonic 
acid) ;  but  so  far  as  hydrocarbons  were  concerned  he  could 
only  prove  the  presence  of  ethane  and  ethylene. 

Besides  the  alkali  salts,  the  copper,  lead,  manganese,  and 
uranium  salts  were  subjected  to  electrolysis  by  Dupre,3  Wiede- 
mann,4  Despretz,5  and  Smith.6  The  metals  were  precipitated 
on  the  cathode,  a  portion  of  the  manganese  and  lead  in  the  form 
of  superoxides. 

Elbs,7  by  the  electrolysis  of  lead  diacetate  in  glacial-acetic- 
acid  solution,  obtained  at  the  anode  crystallized  lead  tetracetate : 
2(CH3COO)2Pb  =Pb  +  (CH3COO)4Pb. 

Fused  potassium  acetate,  according  to  the  experiments  of 
Lassar-Cohn,8  yields  at  the  cathode  methane,  hydrogen,  and 

1  Journ.  prakt.  Chem.  [2]  4,  46  (1871). 
Ann.  chim.  phys.  [4]  14,  157  (1868). 
Arch.  d.  scienc.  phys.  et.  nat    (Geneva)  85,  998  (1871). 
Poggend.  Ann.  104,  162  (1858). 
Compt.  rend.  45,  449  (1857). 
Amer.  Chem.   Journ.  7,  329  (1885).     Electrochemical  Analysis  (Smith) , 

p.  94. 

Ztschr.  f.  Elektrochemie  3,  70  (1896). 
Lieb.  Ann.  251,  358  (1889). 


82  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

carbon;  at  the  anode  carbon  dioxide.  This  result  has  recently 
been  substantiated  by  Berl,1  who  also  proved  by  special  experi- 
ments that  this  decomposition  is  the  result  of  the  action  of 
the  potassium,  set  free  cathodically,  on  the  fused  potassium 
acetate. 

Very  careful  and  comprehensive  experiments  on  the  elec- 
trolysis of  the  alkali  salts  of  organic  acids  have  very  recently 
been  made  by  Petersen.2  The  latter  made  exact  analyses  of 
the  gases  occurring  at  the  electrodes  and  thereby  obtained  an 
insight  into  the  quantitative  course  of  the  reactions,  and  deter- 
mined their  nature. 

Petersen3  was  enabled  to  wholly  confirm  the  earlier  state- 
ments regarding  the  electrolysis  of  acetic  acid  by  Murray,4 
who  investigated  the  influence  of  the  concentration,  current 
strength,  and  temperature  upon  the  course  of  the  electrolysis 
and  found,  like  earlier  investigators,  carbonic  acid,  oxygen, 
hydrogen,  ethane,  and  methyl  acetate.  Murray  disputes  only 
the  occurrence  of  ethylene  .  which  Kolbe  and  Kampf  declare 
they  found. 

Petersen,  however,  clearly  proved  the  presence  of  the 
latter  in  small  quantities^  and  expressed  the  decomposition  of 
acetic  acid  by  the  following  equations: 

I.  2CH3COOH  =2CH3COO +H2. 
II.  2CH3COO + H20  =  2CH3COOH  +  0. 
III.  2CH3COO  =  C2H6+2C02. 
IV.  2CH3COO=CH3COOCH3+C02. 
V.  2CH3COO  +  0=C2H4  +  H20+2C02. 

In  general,  equations  I  and  III  predominate;  V  is  always 
only  traceable. 

Hofer  and  Moest  5  report  upon  the  formation  of  alcohols  in 
the  electrolysis  of  salts  of  fatty  acids. 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  37,  325  (1904). 

2  Ztschr.  f.  phys.  Chem.  33,  90,  295,  698  (1900). 
s  Ibid.  108  (1900). 

4  Journ.  of  the  Chem.  Soc.  61,  10  (1892). 

6  Lieb.  Ann.  323,  284  (1902).     D.  R.  P.  No.  138442  (1901). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  83 

They  found  that  copious  quantities  of  methyl  alcohol,  but 
no  perchloric  acid  esters,  were  produced  by  the  electrolysis  of 
a  mixture  of  sodium  acetate  and  sodium  perchlorate.  The 
reaction  takes  place  in  the  same  manner  as  in  the  case  of  some 
homologues  of  acetic  acid,  and  it  was  found  that  an  addition 
of  alkali  sulphate  or  carbonate  acts  like  the  perchlorate. 

The  general  nature  of  the  reaction  is  that  the  carboxyl 
group  is  replaced:  by  hydroxyl,  so  that  an  alcohol  is  formed 
having  one  carbon  atom  less  than  the  acid;  thus  methyl  alcohol 
is  obtained  from  acetic  acid: 

CH3COO  +  OH  =  CH3OH + C02. 

The  hydroxyl  ion  can  be  derived  from  the  water,  or  be  formed 
in  the  regeneration  of  the  inorganic  acid  acting  as  electrolyte: 

C104 + HOH  =  HC104 + OH. 

The  formation  of  methyl  alcohol  can  hence  be  formulated  as 
follows : 

CH3COO  +  C104 + H20  =  CH3OH  +  HC104 + C02. 

If  the  electrolysis  is  carried  out  between  platinum  electrodes 
without  diaphragms  but  with  continual  stirring,  up  to  90% 
of  the  theoretical  yield  of  methyl  alcohol  can  be  obtained  from 
acetic  acid  and  the  above-mentioned  inorganic  salts. 

The  method  can  also  be  employed  in  the  preparation  of 
formaldehyde,  since  the  methyl  alcohol  on  further  oxidation 
is  converted  into  formaldehyde  (see  p.  58). 

Quite  recently  Forster  and  Piguet  1  have  investigated  the 
electrolysis  of  potassium  acetate,  using  various  anodes.  In 
the  earlier  experiments  polished  platinum  had  served  as  the 
anode.  Iridium  gives  the  same  results  as  platinum;  with  iron 
and  palladium  anodes,  however,  not  a  trace  of  ethane  is  formed, 
but  essentially  an  evolution  of  oxygen  occurs  besides  the 
oxidation  of  the  acetic  acid  to  carbon  dioxide.  At  platinized 
platinum  electrodes  there  occurs,  depending  upon  the  current 
tension,  either  an  evolution  of  oxygen  and  oxidation  to  carbonic 
acid  (no  ethane  being  formed),  or  ethane  is  produced,  with 

1  Ztschr.  f.  Elektrochemie  10,  729  (1904). 


84  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

very  little  evolution  of  oxygen  and  a  very  considerable  oxida- 
tion of  the  acetic  acid  to  carbon  mon-  and  dioxide. 
Forster  and  Piguet  recognize  three  processes: 

1.  Evolution  of  oxygen. 

2.  Oxidation  of  the  acetic  ester  formed  to  carbon  dioxide 
or  carbon  monoxide. 

3.  Formation  of  ethane. 

They  find  that  the  anode  potential  determines  the  effect. 
The  first  reaction,  which  occurs  predominatingly  at  iron  and 
palladium  electrodes,  requires  the  lowest  potential.  With 
platinized  platinum  electrodes  the  potential  lies  higher;  the 
oxidation  action  can  exceed  the  evolution  of  oxygen;  and  with 
a  particularly  high  potential,  which  is  obtained  by  prepolarizing 
the  platinized  anode,1  ethane  is  produced.  With  polished  plati- 
num and  iridium  anodes  the  potential  is  still  higher  than  with 
prepolarized  platinized  platinum  anodes.  Thus  the  production 
of  ethane  predominates  over  the  oxidation  of  acetic  ester. 

Regular  fluctuations  of  the  anode  potential,  which  often  occur 
in  electrolysis,  seem  to  point  to  the  formation  of  transition 
resistances  by  intermediately  occurring  phases  of  poor  conduc- 
tivity (acetic  acid,  acetic  anhydride). 

The  presence  of  free  alkali  is  always  injurious  to  the  pro- 
duction of  ethane.  The  evolution  of  oxygen  at  platinized  plati- 
num increases  with  increasing  alkalinity  and  decreases  at 
polished  anodes,  while  the  oxidation  of  acetic  ester  increases. 

Hofer  and  Moest  2  call  'attention  to  the  great  part  which 
the  production  of  the  methyl  alcohol  demands  in  the  oxida- 
tion effects,  and  which  Forster  and  Piguet  have  neglected  to 
point  out.  They  formulate  the  principal  processes  in  the 
following  manner  : 


1. 

2. 
3. 

CH3 
CH3 
CH3 
OH' 
CH3 
CH3COO' 

!COO'°  + 
ICOO' 
Q2  + 
iCOO' 

=  CH3OH  +  C02, 
=  CH3COOCH3  +  C02. 

1  S.  Friessner,  Zeitschr.  f.  Elektrochem.  10,  270  (1904). 

2  Ztschr.  f.  Elektrochem.  10,  833  (1904). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  85 

An  impartial  decision  has  not  yet  been  given  as  to  whether 
the  ethane  production  depends  upon  a  direct  union  of  the 
anions  or  upon  the  oxidation  of  an  intermediate  product, 
like  acetic  acid,  acetic  anhydride,  or  acetyl  super  oxide. 

Monochloracetic  Acid,  according  to  Kolbe,1  is  reduced  to 
acetic  acid,  hydrochloric  acid  being  split  off;  at  the  same  time 
free  chlorine  is  evolved  (Bunge  2). 

Sodium  Dichloracetate  yields,  besides  carbon  mon-  and  dioxide 
and  oxygen,  a  very  easily  decomposable  oil  containing  chlorine, 
whose  nature  has  not  yet  been  made  clear.  (Troeger  and 
Ewers.3) 

Trichlor acetic  Acid  was  electrolyzed  by  Elbs  and  Kratz  4 
as  sodium  or  zinc  trichlor  acetate.  Trichlor  ace  tic  trichlor- 
methyl  ester  was  formed : 

2CC13COO  =  CC13COOCC13 +2C02. 

Potassium  Cyanacetate. — With  this  Moore  5  obtained  at  the 
positive  pole  carbon  dioxide,  besides  traces  of  nitrogen  and 
ethylene  cyanide ;  at  the  negative  pole  hydrogen  and  potassium 
hydroxide,  bodies  analogous  to  those  obtained  in  the  decom- 
position of  sodium  acetate. 

Thioacetic  Acid. — On  electrolysis  this  gives  acetyl  disul- 
phide  at  the  anode  (Bunge  6) : 

2CH3COSH  =  CH3COS 

|+H2. 
CH3COS 


1  Lieb.  Ann.  69,  279  (1849). 

2  Jorn.  russ.  chem.  Gesellsch.  1,  690  (1892);   see  also  Troeger  and  Ewers, 
Journ.  f.  prakt.  Chem.  58,  121  (1898). 

3  Journ.  f.  prakt.  Chem.  58,  121  (1898). 

4  Ibid.  [2]  55,  502  (1897). 

5  Ber.  d.  deutsch.  chem.  Gesellsch.  4,  519  (1871). 

6  Ibid.  3,  297  (1870). 


86  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Propionic  Acids. 

Propionic  Acid.  —  The  electrolysis  of  a  concentrated  solution 
of  sodium  propionate  was  carried  out  by  Jahn  l  and,  when 
density  of  the  currents  employed  was  not  too  great,  yielded 
hydrogen,  ethylene,  and  carbon  dioxide,  but  little  butane, 
the  quantity  of  which  further  decreased  when  the  electrolyte 
was  diluted.  This  result  Petersen  2  confirmed.  The  evolution 
of  oxygen  increases  as  the  butane  yield  decreases.  The  amount 
of  ethylene  increases  with  increased  dilution  up  to  a  maximum, 
which  is  reached  at  a  concentration  of  the  electrolyte  corre- 
sponding to  about  14%  potassium  propionate.  On  further 
dilution  it  again  decreases.  Petersen  2  also  found  that  ethyl 
propionate  is  always  produced,  corresponding  to  the  analogous 
process  in  the  case  of  acetic  acid.  He  expresses  the  course  of 
the  electrolysis  by  the  following  equations: 


II.  2C2H5COO  +  H20  =  2C2H5COOH  +  0. 
III. 
IV. 
V. 


Miller  and  Hofer  3  have  been  successful  in  introducing 
iodine  into  propionic  acid  by  electrolyzing  an  aqueous  solution 
of  sodium  propionate  and  potassium  iodide. 

Ethyl  alcohol  can  be  obtained  in  small  quantity  from 
sodium  propionate  and  sodium  perchlorate  in  concentrated 
solution  (Hofer  and  Moest  4)  in  the  same  manner  as  methyl 
alcohol  and  formaldehyde  are  formed  from  acetic  acid  and 
perchlorate  : 

C2H5OH+C02. 


1  Wied.  Ann.  (N.  F.)  37,  430  (1889);  see  also  Bunge:  Chem.  Centralblatt  1, 
382  (1890). 

2  Ztschr.  f.  phys.  Chem.  33,  110  (1900). 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  28,  2436  (1895). 

4  Lieb.  Ann.  323,  284  (1902). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  87 

Acetaldehyde  is  formed  as  the  oxidation  product  of  the  latter. 

Sodium  a-Dichlorpropionate  behaves  analogously  to  sodium 
trichlor  acetate  (Troeger  and  Ewers  1).  There  is  formed, 
besides  carbonic  acid  and  oxygen,  the  crystalline  a-dichlor- 
propionic  a-dichlorethyl  ester: 


Sodium  £l-iodopropionate,  according  to  the  last-named 
investigators,  yields  a  little  iodoform  besides  iodine;  the  gases 
formed  are  principally  carbonic  acid.  Carbon  monoxide  and 
oxygen  occur  only  in  small  quantity. 

Butyric  Acids. 

Butyric  Acids.  —  The  two  butyric  acids  were  eiectrolyzed 
by  Bunge.2  With  isobutyric  acid  it  was  not  possible  to  obtain 
hexane,  but  the  normal  acid  yielded  some  butane  besides  larger 
quantities  of  propylene. 

Careful  and  reliable  investigations  on  the  electrolysis  of 
the  potassium  salts  of  butyric  and  isobutyric  acids  have  been 
published  by  M.  F.  Hamonet.3  His  apparatus  consisted  of  a 
copper  beaker  23  cm.  high  and  8  cm.  in  diameter,  which  served 
as  the  cathode.  A  porous  earthenware  cell,  which  contained 
the  anode  and  was  closed  with  a  three-hole  stopper,  stood  in  the 
beaker.  The  perforations  in  the  stopper  held  a  thermometer, 
a  gas-delivery  tube,  and  the  electric  conductor  leading  to  the 
anode.  The  anode  used  in  some  experiments  was  a  platinum 
wire  1  mm.  in  diameter  and  2  m.  in  length;  in  others  a  platinum 
cylinder  14  cm.  high  and  2.5  cm.  in  diameter.  This  variation 
of  current  density  was,  however,  of  secondary  importance. 
Solutions  of  the  potassium  salts  having  a  specific  gravity  of 
1.08-1.19  were  used  as  the  electrolyte.  Current  strengths  of 
4-5  amp.  were  reached  with  a  difference  of  potential  at  the 
poles  of  6-9  volts.  The  electrolysis  was  continued  2-3  hours, 


1  Journ.  f.  prakt.  Chem.  58,  121  (1898). 

2  Journ.  f.  rufcs.  phys.  Gesellsch.  21,  525  (1889). 

3  Comp.  rend.  123,  252  (1893). 


88  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

the  solution  being  kept  cool.  The  following  results  were  ob- 
tained : 

Potassium  Butyrate, 

CH3-CH2.CH2.COOK, 

yielded  225  g.  propylene  bromide  (CH3-CHBr-CH2Br),  corre- 
sponding to  47  g.  propylene  (CH2-CH  =CH2) ;  18  gr.  isopropyl 
alcohol  (CHa-CHOH-CHs);  4.5  g.  butyric  isopropyl  ester 
(CH3>CH2.CH2~COOCH(CH3)2);  and  4.5  g.  complicated  prod- 
ucts, which  became  resinous  when  the  ester  was  saponified  by 
boiling  with  alkali  hydroxide.  Hexane  (CH3-CH2-CH2-CH2 
•CH2-CH3),  and  propyl  alcohol  (CH3  -  CH2  •  CH2OH)  could  not 
be  detected.  They  could,  therefore,  have  been  formed  only 
in  trifling  quantity. 

The  very  remarkable  formation  of  isopropyl  alcohol  can 
only  be  explained  by  assuming  the  hydration  of  propylene 
or  the  molecular  rearrangement  of  the  group  CH3CH2CH2  — . 

Potassium  Isobutyrate, 

(CH3)2:CH.COOK. 

This  salt  gave  300  g.  propylene  bromide  (CH3-CHBr.CH2Br) 
equivalent  to  62.  g  propylene  (CH3-CH:CH2);  26  g.  isopropyl 
alcohol,  (CH3)2:CH-OH;  over  12  g.  isobutyric  isopropyl  ester, 
(CH3)2:CH.COO-CH:(CH3)2;  and  6  g.  of  an  oil  having  a 
pepper-like  odor  and  boiling  at  130°-150°. 

In  this  case  also  the  paraffin  isohexane(CH3)  2 :  CH  •  CH :  (CH3)  2 
was  not  formed. 

Hamonet  draws  the  following  conclusions  from  these  results : 

1.  The  equation 

2CnH2n+1  -COO  =C2nH4n+2 +2C02, 

representing  the  reaction  in  the  electrolysis  of  the  alkali  salts 
of  the  fatty  acids,  which  since  the  experiments  of  Kolbe  has 
been  almost  universally  accepted,  can  no  longer  claim  to  repre- 
sent the  truth  in  the  case,  since  no  or  almost  no  paraffins  result 
from  this  operation. 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  89 

2.  The  olefine  CnH2n  -sometimes  predominates  among  the 
products  formed  by  the  electrolysis  of  the  alkali  salts  of  the 
fatty  acids, 

C»H2n+iCOOK. 

The  general  nature  of  the  reactions  is  represented  by  the 
following  equation: 

2CwH2n+ ! .  COO  =  CnH2n+  x  •  COOH  +  C  nH2n  +  C03, 

3.  An  alcohol  with  n  carbon  atoms  is  always  formed  if 
the  acid  contains  (n-hl)  carbon  atoms.     The  structure  of  the 
alcohol   is   not   always   that   which   is   expected.    Frequently 
more  than  a  third  of  the  energy  of  the  current  is  expended  in 
the  formation  of  the  alcohol.     Whether  the  alcohol  is  generated 
by  the  saponification  of  the  ester  present,  according  to  the 
equation 

2CnH2n+  x  •  COO  =  CnH2n+ !  •  COOCnH2n+ 1  +  C02, 

or  whether  it  is  formed  by  the  hydration  of  the  olefmes, 
C«H2w  +  H20=CnH2n+iOH,  is  still  uncertain.  (Compare  the 
explanation  of  Hofer  and  Moest,  p.  84.) 

A  more  thorough  investigation  of  the  substances  resulting 
from  the  electrolysis  of  compounds  possessing  higher  molecular 
weights  is  yet  wanting. 

Petersen 1  was  able  to  obtain  n-hexane  and  propyl  butyrate 
in  small  quantity  from  butyric  acid;  from  isobutyric  acid  he 
got  diisopropyl  (isohexane)  in  addition  to  the  products  observed 
by  Hamonet. 

If  butyric  acid  is  electrolyzed  with  perchlorate,  according 
to  the  procedure  of  Hofer  and  Moest,2  hexane  is  the  prepon- 
derating product;  there  are  also  obtained  propyl  alcohol  and. 
its  oxidation  product,  propionic  aldehyde: 

CH3CH2CH2COO  +  OH  =CH3CH2CH2OH  +C02. 

1  Bull.  d.  1'Acad.  roy.  de  Danemark  (1897)  397;  Ztschr.  f  phys.  Chera.  33^ 
115  (1900). 
fl.  c. 


90  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Isobutyric  acid  yields,  accordingly,  isopropyl  alcohol  and 
acetone. 

Trichlorbutyric  Acid. — According  to  Troeger  and  Ewers,1 
a  tetrachlorhexyleneglycol  is  formed  at  the  anode  from  sodium 
aa/?-trichlorbutyrate.  The  authors  assume  the  following  equa- 
tions from  this  process: 

I.  2CH3-CHC1  -0012000  = 

CH3  •  CHOI  •  CC12  -  CC12  •  CHC1  -  CH3  +  2CO , : 
II .  CH3  •  CHC1  •  CC12  -  CC1*  •  CHC1  •  CH:,  +  2H,0 
=  CH3CHOH  -  CC12  •  CC12  •  CHOH  •  CH,  +  2HC1.. 

Accordingly,  a  hexachlorhexane  would  be  first  formed  in 
a  normal  manner,  C02  being  split  off ;  secondarily,  the  two  very 
mobile  /^-chlorine  atoms  would  be  torn  away  by  water,  hydro- 
chloric acid  and  tetrachlorhexyleneglycol  resulting. 

Valeric  Acids. 

Valeric  Acids. — Kolbe 2  electrolyzed  the  potassium  salt  of 
isovaleric  acid  in  concentrated  aqueous  solution  and  obtained 
as  chief  product  octane  (dissobutane) : 

CHsy  /CH3 

>CH.CH2.CH2.CH< 
CH/  XCH3 

Besides  this  there  appeared  as  decomposition  products 
hydrogen,  carbonic  acid,  butylene,  and  the  butyl  ester  of  valeric 
acid. 

Brester,3  who  performed  his  experiments  under  different 
conditions,  obtained  at  the  anode  a  gaseous  mixture  of  carbon 
dioxide,  butylene,  and  oxygen. 

Petersen  4  subjected  the  behavior  of  both  acids  to  a  thorough 
investigation.  He  established  the  formation  of  normal  octane 
and  butyl  valerate  in  the  decomposition  of  n-valeric  acid;  among 

1  Journ.  f.  prakt.  Chem.  59,  464  (1899). 
2Lieb.  Ann.  69,  257  (1849). 
3  Jahresb.  f.  Chem.  86  (1859),  757  (1866). 
«  Ztschr.  f.  phys.  Chem.  33,  295  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  91 

the  evolved  gases  butylene  and  also  hydrogen  and  oxygen 
were  found.  A  small  quantity  of  butyl  alcohol,  which  was  fur- 
ther oxidized  to  butyric  aldehyde,  was  also  formed  by  the 
saponificatlon  of  butyl  valerate. 

The  oil  which  is  formed  in  the  electrolysis  of  potassium 
isovalerate  is  composed  of  diisobutyl  and  trimethylmethyl 
isovalerate,  besides  a  small  ,  quantity  of  isobutyl  isovalerate 
and  isobutyric  aldehyde.  By  saponification  of  the  ester,  tri- 
methylcarbinol  accompanied  by  a  trifling  quantity  of  isobutyl 
alcohol  is  found  in  the  solution. 

/?-butylene  and  isobutylene  could  be  detected  in  the  evolved 
gases. 

Petersen  adduces  the  following  equations  of  reactions  as 
the  predominating  ones: 

I.  2(CH3)2:CH.CH2.COOH=2(CH3)2:CH.CH2.COO  +  H2; 
II.  2(CH3)2:CH.CH2-COO  +  H20 

=  2(CH3)2:CH.CH2.COOH  +  0; 

III.  2(CH3)2:CH.CH2.COO=[(CH3)2:CH-CH2]2+2C02; 

IV.  2(CH3)2:CH-CH2.COO 

-  (CH3)  2  :  CH  •  CH2  •  COO  -  C  :  (CH3)  3  +  C02  ; 
V.  2(CH3)2:CH.CH2.CXXHO 

=  (CH3)2:C:CH2+CH3.CH:CH 


To  the  above  may  be  added  the  following  equations  of  minor 
importance  ; 

VI.  (CH3)2:CH.CH2.COO.C!(CH3)3+H20 

=  (CH3)  2  :  CH  .  CH2  •  COOH  +  (CH3)  3  :  COH  ; 
VII.  (CH3)2:CH-CH2.COO.CH2.CH:(CH3)2  +  H20 

=  (CH3)  2  :  CH  •  CH2COOH  +  (CH3)  2  :  CH  -  CH2OH  ; 
VIII.  (CH3)  2  :  CH  -  CH2OH  +  0  =  (CH3)  2  :  CH  •  COH  +  H20. 

Even  this  complicated  scheme  cannot  claim  to  be  complete. 
Probably  some  entirely  different  reactions  which  have  thus 
far  not  been  elucidated,  occur  also.  Considerable  differences 
between  the  yields  theoretically  expected  and  those  actually 
obtained  point  to  such  a  supposition. 


92  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Trimethylacetic  Acid  (Pivalic  acid)  —  the  third  of  the  valeric 
acids  —  has  also  been  investigated  by  Petersen.  It  yields 
irimethylcarbinol  and  probably  hexamethylethane,  besides  an 
isomeric  body,  and  also  two  isomeric  butylenes,  isobutylene 
predominating  with  perhaps  also  /?-butylene.  Aldehyde  is  not 
formed;  neither  is  an  ester  formed. 

The  principal  processes  taking  place  are  the  following: 


II.  2C(CH3)  3COO  +  H20  -  2C(CH3)  3COOH  +  0  ; 

III.  2C(CH3)3COO=C(CH3)3.C(CH3)3+2C02; 

IV.  2C(CH3)  3COO  +  0=  2(CH3)  2C  :  CH2  +  H20  +  2C02. 

The  trimethylcarbinol,  a  secondary  product,  is  probably 
formed  1  by  .the  addition  of  water  to  the  isobutylene. 

The  electrolysis  of  these  three  isomeric  acids  affords  thus 
•considerable  qualitative  differences  in  the  results.  Summing 
up  the  whole  matter,  it  can  be  said  that  the  electrolysis  of  a 
valeric  acid  gives  octane,  butyl  valerate,  butylene,  butyl  alco- 
hol, and  butyric  aldehyde. 

1.  The  normal  valeric  acid  yields  normal  compounds  exclu- 
sively. 

2.  Isovaleric  acid   gives  diisobutane,  t  rime  thylme  thy  1   iso- 
valerate,  and  trimethylcarbinol,  also    a   little  isobutyl  isoval- 
erate,  isobutyl  alcohol,  and  isobutyric   aldehyde,  and,  finally, 
two  isomeric  butylenes,  isobutylene  and  /2-butylene. 

The  products  resulting  from  the  electrolysis  of  trimethyl- 
acetic  acid  have  been  summarized  above. 

The  fourth  isomeric  valeric  acid  (active),  ethylmethylacetic 
acid,  has  not  yet  been  investigated. 

n-Caproic  Acid.  —  A  concentrated  solution  of  the  potassium 
salt  gave  decane,  and  traces  of  the  amyl  ester  of  caproic  acid, 
both  of  which  are  normal  decomposition  products.  The 
electrolyses  were  made  by  Brazier  and  Gossleth,2  and  by  Wurtz.3 

1  Ztschr.  f.  phys.  Chemie  33,  716  (1900), 

2Lieb.  Ann.  75,  265  (1850). 

8  Ann.  chim.  phys.  [3]  44,  291  (1855). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  93 

The  electrolytic  relations  in  the  decomposition  of  caproic 
acid -were  investigated  by  Rohland,1  who  electrolyzed  the  alkali 
salt.  He  obtained  normal  decane,  CioH22. 

Petersen  2  investigated  the  electrolysis  of  potassium  capro- 
ate  on  a  larger  scale.  The  oil  which  separated  during  the 
passage  of  the  current  consisted  of  normal  decane,  a  little 
amyl  caproate  and  amyl  alcohol,  a  trifling  quantity  of  amylene, 
and  an  aldehyde,  probably  CH3(CH2)3COH.  The  greater 
quantity  of  the  amylenes  formed  during  the  electrolysis 
was  found  in  the  gaseous  mixture;  isopropylethylene, 
(CH3)2CHCH:CH2,  was  probably  present  with  the  normal 
amylene,  CH3CH2CH2CH :  CH2. 

n-Heptylic  Acid,  Oenanthylic  Acid. — The  normal' acid  was 
electrolyzed  by  Brazier  and  Gossleth,3  under  conditions  similar 
to  those  for  caproic  acid,  and  gave  two  hydrocarbons, 
Ci2H26  and  Ci2H24,  in  addition  to  hydrogen,  potassium  car- 
bonate, and  acid  potassium  carbonate. 

On  electrolyzing  a  concentrated  solution  of  potassium 
n-heptylate,  Rohland 4  obtained,  besides  dodecane,  Ci2H2e,  a 
small  quantity  of  a  mixture  of  unsaturated  hydrocarbons  of  the 
series  CnH2n  boiling  at  145°. 

n-Caprylic  Acid. — Rohland 5  electrolyzed  a  concentrated 
potassium-salt  solution  of  this  acid  and  obtained  the  hydro- 
carbon tetradecane,  CuH3o. 

Pelargonic  Acid,  under  similar  conditions,  gives  the  hydro- 
carbon dioctyl. 

The  formation  of  olefines,  in  the  electrolysis  of  aliphatic 
monocarboxylic  acids,  depends,  perhaps,  not  upon  an  oxidation 
process, 

2CnH2n+1COO +0  =2C»H2n  +  H20  +2C02, 


1  Ztschr.  f.  Elektrochemie  4,  120  (1897). 

2  Ztschr.  f.  phys.  Chem.  33,  317  (1900). 

3  Lieb.  Ann.  75,  265  (1850). 

4  Ztschr.  f.  Elektrochemie  4,  120  (1897). 
6  I.e. 


94  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

but  upon  a  mutual  reaction  of  the  anions,  analogously  to  that 
which  causes  the  formation  of  saturated  hydrocarbons: 


II.  2CnH2n+1COO=CnH2n+1COOH+CnH2n+C02. 

The  occurrence  of  secondary  or  tertiary  alcohols  depends 
presumably  upon  the  addition  of  water  to  the  defines: 

CnH2n  +H20  =  CnH2n+iOH. 

According  to  Petersen,1  the  equations  expressing  the  general 
decomposition  of  aliphatic  acids  are  the  following: 

I.  2CnH2n+iCOOH=2CnH2n+1COO+H2; 
II.  2CnH2n+iCOO+H20=2CnH2n+1COOH+0; 

III.  2CnH2n+iCOO=C2nH4n+2+2C02; 

IV.  2CnH2n+1COO  =CrJH2n+iCOOCnH2n+1  +C02; 
V.  2CnH2n+iCOO  =  CnH2n+iCOOH+CnH2n+C02; 

VI.    CnH2n  +H20  =CnH2n  +  lOH;  )   Secondary 

VII.    CnH2n+CnH2n  +  lCOOH  =CnH2n  +  iCOOCnH2n  +  i.  )      tertiary. 


Of  the  unsaturated  monocarboxylic  acids,  undecylenic  acid 
and  oleic  acid  have  been  investigated  by  Rohland.2  Both 
yielded,  on  electrolyzing  their  potassium  salts  in  aqueous  solu- 
tion, a  mixture  of  unsaturated  hydrocarbons,  the  nature  of 
which  was  not  determined. 

Electrolysis  of  Mixtures.  —  Wurtz  3  was  the  first  to  conceive 
the  extremely  fruitful  idea  in  electrosynthesis  of  making  syn- 
theses of  substances  with  mixed  radicals  by  electrolyzing  two 
components.  After  discovering  his  hydrocarbon  synthesis, 
which  depends  upon  the  action  of  sodium  upon  alkyl  iodides, 
and  the  use  of  the  method  in  the  preparation  of  "  mixed  radi- 
cals "  from  two  different  alkyl  iodides,  he  also  tried  to  obtain 


1  Ztschr.  f.  phys.  Chem.  33,  720  (1900). 
21.  c. 


8  Ann.  chim.  phys.  [3]  44,  275  (1855);  Jahresb.  f.  Chem.  1855,  575. 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  95- 

mixed  hydrocarbons  by  electrolyzing  the  salts  of  fatty  acids, 
using  Kolbe's  hydrocarbon  synthesis: 

RiCOO  +R2COO  =  RiR2 +2C02. 

The  successful  results  of  these  experiments  prompted  various 
investigators  to  select,  as  the  materials  for  the  starting-point 
of  their  electrolysis,  mixtures  of  substances  whose  electrolytic 
intermediate  products  could  mutually  react,  v.  Miller  and  Hofer 
made  use  of  these  forms  of  reactions  in  the  fatty-acid  series 
for  accomplishing  the  syntheses  of  acids.  Lob  in  a  similar 
manner  prepared  mixed  azo-compounds  in  the  aromatic  series. 
The  following  are  the  experiments  made  by  Wurtz : 

Potassium  acetate  and  potassium  cenanthylate  yield  trifling 
quantities  of  heptane  (methylcaproyl,  Wurtz) : 

CH3COO  +  COO  •  (CH2)  5  •  CH3  =  CH3  •  (CH2)  5  •  CH3  +  2C02. 

Potassium  valerate  and  potassium  cenanthylate  give  the  ex- 
pected mixed  hydrocarbon,  a.  decane,  as  chief  product  (butyl- 
caproyl,  Wurtz) : 

(CH3)  2 :  CH  -  CH2  -  COO  +  COO  -  (CH2)  5  -  CH3 

=  (CH3)  2 :  CH  •  (CH2)  6  •  CH3  +  2C02. 

There  are  formed  also  a  little  octane,  dodecane,  and  un- 
saturated  hydrocarbons. 

In  the  following  discussion  the  description  of  the  electrolysis 
of  mixtures  is  given  under  the  heading  of  the  highest  hydro- 
carbon component,  since  the  reaction  in  electrolysis  depends 
upon  the  nature  of  the  components  of  the  mixtures;  thus 
the  behavior  of  each  separate  component  will  then  have  been 
previously  described. 

II.  Monobasic  Alcohol-  and  Ketonic  Acids. 

a.  Alcohol-  (Hydroxy-)  Acids. 

While  the  acid  anions  of  the  unsubstituted  aliphatic  mono- 
carboxylic  acids  react  preponderatingly  by  splitting  off  carbonic 


96  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

acid,  without  further  oxidation  of  the  radical  united  to  the 
carboxyl  group,  the  anion  of  the  hydroxy-acids  is  regularly 
oxidized  further.  The  extent  of  the  oxidizing  action  depends, 
among  other  circumstances,  to  a  great  extent  upon  the  con- 
centration. For  example,  gly  collie  acid  in  concentrated  solu- 
tions is  oxidized  almost  completely  to  formaldehyde,  and  to  a 
less  extent  to  formic  acid  and  carbonic  acid.  By  increasing 
the  dilution  carbon  monoxide  occurs  in  place  of  formaldehyde.1 


CH20+C02+H20; 
II.  CH2OHCOO+30H=CO+C02  +  3H20. 

The  substitution  of  methyl  for  hydro  xyl  does  not  affect 
the  easy  oxidability.  It  is  evident  from  the  theoretical  explana- 
tions given  in  the  first  chapter  that  the  changes  in  concentration 
are  of  importance  for  the  course  of  the  reaction  only  in  so  far 
as  they  influence  the  anode  potential.  By  artificially  keeping 
the  latter  constant,  the  products  must  remain  the  same,  being 
independent  of  the  conditions  of  concentration.  In  general, 
the  following  rules  can  be  adduced  for  the  electrolysis  of 
oxy-acids  (chiefly  worked  out  by  Miller  and  Hofer,2  and 
Hamonet  3)  : 

a-Oxy-acids  are  converted  by  electrolysis  in  concentrated 
solution  into  aldehydes  or  ketones.  If  the  solution  is  more 
highly  diluted,  the  compound  is  oxidized  to  carbon  monoxide. 

/9-Oxy-acids  behave  more  like  acetic  acid;  they  are,  at 
least  partially,  converted  into  glycols,  or  their  ethers: 

I.  20H.CnHmCOO=OH.CnHm.CnHm.OH+2C02; 
II. 


In  the  case  of  dioxy-acids  the  oxidation  affects  both  hydroxyl 
groups,  the  intermediate  CHOH-groups  being  oxidized  to 
carbon  mon-  or  dioxide. 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  461  (1894). 

2  Ibid. 

3  Compt.  rend.  132,  259  (1901). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  97 

The  experiments  of  Miller  and  Hofer  were  made  by  passing 
the  electrolyte  in  a  slow  stream  through  the  cell  (Apparatus, 
Fig.  4,  p.  44).  This  made  it  possible  to  find  decomposition  prod- 
ucts which  would  otherwise  have  been  changed  by  further 
electrolysis;  a  more  complete  expression  of  the  course  of  the 
decomposition  was  thus  obtained.  It  is  to  be  regretted  that 
the  researches  do  not  mention  the  necessary  data  regarding 
the  electrical  conditions. 

Glycollic  Acid. — If  a  solution  of  30  g.  sodium  glycollate  in 
38  cc.  water  is  electrolyzed  with  a  current  strength  of  1  amp., 
there  are  formed  chiefly  carbonic  acid  and  formaldehyde, 
besides  a  little  carbon  monoxide,  formic  acid,  and  oxygen 
(Miller  and  Hofer x) .  Walker 2  obtained  aldehyde  in  the 
electrolysis  of  the  sodium  salt  of  ethyl  glycollic  ether. 

Methoxylglycollic  Acid. — The  electrolysis  of  its  sodium  salt 
was  made  by  the  same  authors3  and  yielded  formaldehyde, 
methylal,  formic  acid,  and  carbonic  acid;  hi  dilute  solution  also 
carbon  monoxide  and  a  little  methyl  alcohol. 

A  mixture  of  potassium  glycollate  and  potassium  acetate 
unites  at  the  positive  pole  to  form  ethyl  alcohol  (Miller  and 
Hofer4);  some  acetaldehyde  is  also  formed  by  further  oxida- 
tion: 

CH2(OH)COO  +CH3COO  =CH3CH2(OH)  +2C02. 

Oxypropionic  Acids. 

Ordinary  Lactic  Acid. — As  Kolbe  5  had  already  discovered, 
the  concentrated  solution  of  the  potassium  salt  gave  carbon 
dioxide  and  acetic  aldehyde.  The  investigators  above  men- 
tioned also  observed  the  presence  of  some  formic  acid.  When 
the  solution  surrounding  the  positive  pole  was  kept  slightly 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  467  (1894). 

2  Journ.  Chem.  Soc.  65,  1278  (1896). 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  469  (1894). 

4  Ibid.  28,  2437  (1895). 

6  Lieb.  Ann.  113,  214  (1860). 


98  ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

alkaline,  aldol  and  crotonic  aldehyde  were  formed  instead  of 
acetic  aldehyde. 

Sarcolactic  Acid.  —  When  the  solution  surrounding  the  posi- 
tive pole  was  kept  neutral,  a  concentrated  solution  of  the  sodium 
salt  yielded  acetic  aldehyde  and  carbon  dioxide. 

Hydracrylic  Acid  (Ethylenelactic  Acid  =  /?-oxypropionic  Acid)  . 
—  Resin  and  a  little  formic  acid  were  found  present  in  the 
electrolyte  surrounding  the  positive  pole. 

The  potassium  salt  of  the  alcoholic  amyl  ether  of  this  acidy 
the  /?-amyloxypropionic  acid,  was  electrolyzed  by  Hamonet.1 
It  gave  about  50  per  cent  of  the  theoretical  yield  of  1.4-butan- 
dioldiamyl  ether  (diamyl  ether  of  butylene  glycol). 


Glyceric  Acid  (Dioxypropionic  Acid).  —  This  acid  decom- 
poses into  carbon  mon-  and  dioxide,  formaldehyde,  and  formic 
acid  (Miller  and  Hofer). 

Oxy  butyric  Acids. 

a-Oxybutyric  Acid  (CH3  -  CH2  -  CHOH  •  COOH)  .—  This  sub- 
stance was  converted  into  carbon  dioxide,  propionic  aldehyde, 
and  some  formic  acid  (Miller  and  Hofer). 

a-Oxyisobutyric  Acid  ((CH3)2:  CHOH  -COOH)  .—This  com- 
pound, investigated  in  the  same  manner,  was  found  to  be  par- 
tially oxidized  at  the  anode  to  acetone.  Much  carbonic  acid 
and  a  little  carbon  monoxide  is  also  evolved. 

/9-Oxybutyric  Acid  (CH3  •  CH(OH)  .  CH2  -  COQH)  .—From  this 
acid  were  obtained  in  the  positive  electrolyte  crotonic  aldehyde 
and  a  little  formic  acid,  also  resinous  substances.  Considerable 
quantities  of  carbonic  acid,  also  a  little  carbon  monoxide  and 
unsaturated  hydrocarbons,  are  formed.  The  small  quantities 


.  c. 


[ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  99 

of  saturated  hydrocarbons  are  derived  probably  from  impurities 
in  the  acid  (presence  of  acetic  acid). 

r-Oxybutyric  Acid  (CH2OH  •  CH2  •  CH2  •  COOH)  .—  Hamonet  * 
electrolyzed  the  alkali  salt  of  7--isoamyloxybutyric  acid  in 
order  to  obtain  symmetrical  hexylene  glycol,  or  its  diamyl 
ether.  The  desired  reaction  did  not  take  place: 


2C5CiiOCH2.CH2.CH2-COO 

=  C5Hn  -OCH2- 


/?-Methylglyceric  Acid  (a-/?-Dioxybutyric  Acid  (M.  Pt.  74- 
75°)=CH3-CHOH-CHOH-COOH).— When  the  potassium  salt 
of  this  acid'  is  electrolyzed  (Pissarshewski 2)  it  breaks  up 
into  carbon  mon-  and  dioxide,  formaldehyde,  formic  acid, 
acetaldehyde,  acetic  acid,  and  another  substance  having  the 
property  of  reducing  Fehling's  solution.  This  latter  compound 
was  not  isolated. 

vCH-COOH 

/?-Methylglycidic  Acid,  0<^  |  behaves  similarly. 

XJH-CHa 

b.  Ketonic  Acids. 

Pyroracemic  and  Isevulinic  acid,  i.e.,  an  a-  and  a  f-ketonic 
acid  are  the  only  monobasic  ketonic  acids  which  have  been 
electrolyzed.  The  electrolysis  of  a  representative  of  a  /?-ketonic 
acid,  acetoacetic  acid,  could  not  be  carried  out,  on  account  of 
the  instability  of  the  free  acid  and  its  salts.  The  reactions 
take  place  partly  in  a  manner  similar  to  those  occurring  in  the 
decomposition  of  acetic  acid;  the  anions  unite  to  form  a  dike- 
tone,  carbonic  acid  being  split  off;  and  partly  in  a  further 
oxidation  to  acetic  acid,  with  the  occurrence  of  carbon  mon- 
and  dioxides. 


1  Compt.  rend.  136,  96  (1903). 

2  Ztschr.  d.  russ.  chem.  phys.  Gesellsch.  29,  289,  338  (1897). 


100         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Pyroracemic  Acid. — Potassium  pyroracemate  gives  (Hofer)  l 
chiefly  acetic  acid  and  also  a  little  diacetyl: 

I.  CH3-CO-COO  +  OH=CH3COOH+C02; 
II.  2CH3  -  CO  -  COO  =  CH3  •  CO  -  CO  •  CH3  +  2C02, 

Rockwell 2  found  at  the  anode  some  acetaldehyde,  and 
at  the  cathode  the  normal  reduction  product  of  pyroracertic 
acid,  i.e.  a-lactic  acid: 

CH3  -  CO  •  COOH + H2  =  CH3  -  CHOH  -  COOH  ; 

also  some  propionic  acid,  probably  formed  by  further  reduction, 
Laevulinic  Acid. — This  acid  is  much  better  adapted  for  the 
synthesis  of  the  corresponding  diketone  than  is  pyroracemic 
acid.  Hofer,3  on  electrolyzing  the  potassium  salt  of  the  acid, 
obtained  about  50%  of  the  theoretically  expected  quantity  of 
2.7-octandion : 

2CH3.CO-CH2.CH2-COO 

= CH3  •  CO  -  CH2  •  CH2  •  CH2  .  CH2  •  CO  •  CH3  +  2C02. 

Considerable  quantities  of  acetic  acid  are  also  formed,  and  some 
carbon  monoxide  is  produced  by  the  oxidation  of  the  methylene 
groups. 

Acetoacetic  Acid. — If  the  sodium  compound  of  acetoacetic 
ester  (Weems 4)  in  alcoholic  solution  is  electrolyzed,  there  is 
formed  diacetylsuccinic  ester: 

COCH3         CQCH3 

2CHNa      =2CH          +2  Na 

COOC2H5      COOC2H5 
COCH3 

2  CH  =  C2H5OOC  -  CH  -  CH  •  COOC2H5 

COOC2H5  H3CCO  COCH3. 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  33,  650  (1900). 

2  Journ.  Amer.  Chem.  Soc.  24,  719  (1902). 
M.  c. 

Amer.  Chem.  Journ.  16,  569  (1894). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  101 

According  to  Tafel  and  Friedrichs,1  acetoacetic  ester  can 
be  easily  reduced  in  sulphuric-acid  solution.  This  reduction 
evidently  extends  to  the  carbox-ethyl  group  because  a  molecule 
of  the  ester  requires  almost  six  atoms  of  hydrogen. 

Acetylmalonic  Acid,  CH3  •  CO  •  CH :  (COOH)  2,  and  Acetone- 
dicarboxylic  Acid,  CO :  (CH2COOH)  2,  do  not  permit  their 
anions  to  unite  (Weems2). 

In  connection  with  his  investigation  of  ketonic  acids,  Hof  er  3 
has  used  the  electrosynthetic  reaction,  previously  discovered 
with  Miller,4  which  consists  in  electrolyzing  potassium  salts  of 
organic  acids  in  mixture  with  potassium  acetate  and  other 
lower  fatty  acids.  The  general  nature  of  the  reaction  is  that 
the  two  anions  unite,  as  in  Kolbe's  synthesis,  carbonic  acid 
being  split  off,  e.g., 

R.CO-COO+Ri'COO=R.CO-Ri+2C02. 

Potassium  Pyroracemate  and  Potassium  Acetate  thus  yield 
acetone  as  the  chief  product: 

CHsCOCOO  +CH3COO  =  CH3COCH3  +2C02. 

Some  acetic  methyl  ester  and  traces  of  diacetyl  are  also 
formed. 

Potassium  Pyroracemate  and  Potassium  Butyrate  unite  to 
form  methylpropylketone: 

CH3.CO-COO+CH3.CH2.CH2.COO 

= CH3  •  CO  •  CH2  •  CH2  •  CH3  +  2C02. 

Some  diacetyl  is  also  formed  in  this  case,  with  trifling 
quantities  of  esters  of  butyric  acid,  and  larger  quantities  of 
hydrocarbons,  chiefly  hexane  and  decane.  The  \hexane  was 
formed  from  the  butyric  acid,  the  decane  from  caproic  acid, 
an  impurity  in  the  butyric  acid. 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  37,  3188  (1904). 
21.  c. 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  33,  650  (1900). 

4  Ibid.  28,  2427  (1895). 


102          ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Potassium  Lcevulinate  and  Potassium  Acetate  yield,  analo- 
gously, methylpropylketone : 

CH3  •  CO  •  CH2  •  CH2  •  COO  +  CH3COO 

= CH3  -  CO  •  CH2  •  CH2  •  CH3  +  2C02. 

At  the  same  time  a  larger  quantity  of  2.7-octandion  could  be 
isolated. 

Potassium  Lcevulinate  and  Potassium  Pyroracemate  unite  to 
form  the  expected  ace  tony  lace  tone,  besides  a  little  2.7-octandion: 

CH3  -  CO  •  CH2  •  CH2  -  COO  +  CH3 .  CO  •  COO 

=CH3.CO-CH2.CH2.CO.CH3+2C02. 

III.  Dibasic  Acids. 

Most  beautiful  results  of  the  application  of  electrolytic 
decompositions  in  a  direct  synthesis  have  been  accomplished 
with  dibasic  acids.  The  results  have  a  practical  as  well  as 
a  theoretical  value, — as  useful  methods  of  preparing  com- 
pounds for  the  laboratory,  and  as  proofs  for  certain  constitu- 
tions. The  researches  of  Brown  and  Walker  1  have  opened 
up  an  extremely  fruitful  domain. 

The  dibasic  acids  having  the  constitution 

COOHCCH^COOH, 

when  electrolyzed  as  such  or  as  their  soluble  salts,  discharge 
at  the  anode  the  anions 

COO(CH2)XCOO. 

These  give  hydrocarbons,  mostly  unsaturated  and  in  poor 
yield,  carbonic  acid  being  split  off.  The  reaction  observed  in 
the  case  of  acetates  does  not  here  predominate. 

Simple  and  smooth  reactions,  however,  are  obtained  if  an 
ester  group  is  introduced  into  the  dibasic  fatty  acids.  Since 

ieb.  Ann.  261,  107  (1891);   274,  41  (1893). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  103 

ester  groups,  according  to  an  experiment  of  Guthrie,1  are 
electrolytically  inactive,  the  mono-esters  of  dibasic  acids  behave 
like  monobasic  acids,  i.e.  carbon  dioxide  is  split  off  and  di- 
esters  of  higher  dibasic  acids  are  formed,  saponification  con- 
verting the  esters  into  the  free  dibasic  acids: 


2ROOC(CH2)  XCOO  =  ROOC(CH2)  x  -  (CH2) 

Thus  the  diethyl  ester  of  succinic  acid  is  formed  from  ethyl 
potassium  malonate: 

2C2H5OOCCH2COO  =C2H5OOCCH2CH2COOC2H5  +2C02. 

Von  Miller  and  Hofer  2  broadened  the  possibility  of  the  electro- 
syntheses  of  dibasic  acids  by  borrowing  an  idea  of  Wurtz  and 
using  the  results  of  Brown  and  Walker.  Wurtz,3  as  already 
mentioned,  had  electrolyzed  mixtures  of  two  fatty-acid  salts, 
and  accomplished  the  union  of  the  different  radicals  to  form 
the  corresponding  hydrocarbons.  In  the  same  manner,  von 
Miller  and  Hofer  electrolyzed  mixtures  of  fatty-acid  salts  and 
mono-esters  of  dicarboxylic  acids.  Hereby  the  esters  of  mono- 
carboxylic  acids  containing  a  higher  number  of  carbon  atoms 
are  formed.  If,  for  instance,  a  mixture  of  potassium  acetate 
and  potassium  ethyl  succinate  is  subjected  to  electrolysis, 
butyric  ethyl  ester  is  formed,  according  to  the  following  equa- 
tion: 
CH3COO  +COOCH2CH2COOC2H 

=  CH3CH2CH2COOC2H5  +  2C02. 

If  the  two  carboxyl  groups  of  dibasic  acids  are  esterified, 
such  a  di  ester  can  behave  as  an  acid  only  when  methylene 
groups  possessing  a  decidedly  acid  character  are  present.  Mulli- 
ken4  and  Weems  5  investigated  such  compounds.  The  sodium 

1  Lieb.  Ann.  99,  65,  1856. 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  28,  2427  (1895). 
sjaheresber.  d.  Chem.  575  (1855). 

*  Amer.  Chem.  Journ.  15,  323  (1893). 
5  Ibid  16,569  (1894). 


104         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

compounds  of  diethyl  esters  of  dibasic  acids  in  particular  fre- 
quently behave  in  a  manner  analogous  to  that  of  the  car  boxy  lie 
acids,  the  anions  uniting.  The  same  compounds  are  thus  ob- 
tained as  are  formed  by  the  elimination  of  sodium  by  iodine. 
Thus  sodium  diethylmalonic  ester  gives  e thane tetracarboxy lie 
ester; 

COOC2H5      COOC2H5 

2CHNa      =2CH-       +2Na 

C002H5        COOC2H5 

i 

COOC2H5      COOC2H5      COOC2Hr 
2  CH-          =CH-          -CH 
!OOC2H5      COOC2H5      COOC2H5. 


•    \*s 

i, 


If  the  methylene  groups  of  dicarboxylic  acids  contain 
electrolytically  sensitive  radicals,  the  reaction  picture  is  shifted, 
as  will  be  touched  upon  in  the  special  cases. 

Oxalic  Acid. — The  deportment  of  the  saturated  solution 
of  the  free  acid  on  electrolysis  was  determined  by  Brester,1 
Bourgoin,2  Balbiano  and  Alessi,3  Bunge,4  and  Renard.5  The 
general  result  was  that  oxygen  and  carbon  dioxide  were  obtained 
at  the  anode  and  hydrogen  at  the  cathode.  It  is  possible  to 
completely  oxidize  oxalic  acid  to  carbon  dioxide.  On  this 
property  depends  the  greal  importance  of  oxalic  acid  in  quanti- 
tative electrolytic  analysis,  into  which  it  has  been  introduced 
by  Classen.6 

The  ability  of  ammonium  oxalate  to  form  soluble  double 
salts  with  many  difficultly  soluble  or  insoluble  metallic  salts 
is  in  accord  with  the  favorable  conduct  of  the  acid  on  electroly- 

1  Jahresb.  f.  Chem.  87  (1866). 
2Compt.  rend.  67,  97  (1868). 

8  Gazz.  chim.  12,  190  (1882);  Ber.  d.  deutsch.  chem.  Gesellsch.  15,  2236 
(1882). 

4  Ber.  d.  deutsch.  chem.  Gesellsch.  9,  78  (1876). 

•Ann.  chim.  phys.  [5]  17,  289  (1878). 

•Classen,  Quan.  Analysis  by  Electrolysis  (Wiley  &  Sons,  N.  Y.). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  105 

sis,  by  which  operation  it  may  be  entirely  removed  from  the 
solution  in  the  form  of  gas. 

The  reducing  effects  of  the  current  on  oxalic  acid  were  also 
observed.  Thus  on  electrolyzing  both  the  free  acid  and  its 
sodium  salt  Balbiano  and  Alessi  were  able  to  prove  the  presence 
of  glycollic  acid.  Tafel  and  Friedrichs  1  obtained  a  good  yield 
of  glyoxylic  acid  by  reducing  oxalic  acid  in  sulphuric-acid 
solution  at  lead  or  mercury  cathodes.  Oxalic  ester  and  oxal- 
acetic  ester  are  easily  reduced  also. 

The  oxidation  is  not  complete  if  the  electrolysis  is  conducted 
in  the  cold  solution,  carbon  monoxide  as  well  as  carbon  dioxide 
being  then  formed  at  the  positive  pole. 

The  decomposition  reactions  of  oxalates  are  entirely  analo- 
gous to  those  of  the  free  acid.  In  alkaline  solution  the  oxidation 
proceeds  more  rapidly  than  in  neutral  solution  because  of  the 
better  conductivity  of  the  alkalies. 

Naturally  ethyl  potassium  oxalate  cannot  react  in  accord- 
ance with  the  scheme  of  the  Brown  and  Walker's  synthe- 
ses. When  it  was  electrolyzed  both  investigators2  observed 
the  presence  of  ethylene.  This  unsaturated  hydrocarbon  was 
very  likely  derived  from  the  ester  group. 

Petersen3  has  formulated  the  following  equations  of  decom- 
position: 


I.  (COOH)2=(COO)2 
II.  (COO)2  +  H20=(COOH)2 

III.  (COO)2  =  2C02; 

IV.  (COOH)2  +  0  = 


These  data  on'  the  electrolysis  of  oxalic  acid  must  be  sup- 
plemented by  those  regarding  its  reduction  to  glycollic  acid, 
glyoxylic  acid,  and  the  reduction  to  formic  acid  (Royer  4), 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  37,  3189  (1904). 

2  Lieb.  Ann.  274,  70  (1893). 

3  Ztschr.  f.  phys.  Chem.  33,  698  (1900). 
4Compt.  rend.  69,  1374  (1869),  70,731  (1870). 


106         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

which  is  brought  about  when  using  oxalic  acid  in  place  of  nitric 
acid  in  a  Grove  cell. 

A  series  of  researches  concerning  the  relation  between  the  oxi- 
dation of  oxalic  acid  and  the  electrical  conditions  have  been 
made.  Oettel 1  discovered  that  the  current  consumption 
required  for  an  oxidation  process  is  greater  when  a  smaller 
current  density  is  used  than  when  a  higher  density  is  employed. 
Acker  berg  2  determined  that  the  oxidation,  which  is  trifling  at 
a  polished  platinum  anode,  is  quantitative  under  the  same  con- 
ditions at  a  platinized  anode.  Salzer  3  investigated  the  elec- 
trolysis of  oxalic  acid,  as  to  the  tension  conditions  and  oxida- 
tion action,  in  sulphuric-acid  and  in  aqueous  solutions  at  polished 
(bright)  and  platinized  anodes. 

Malonic  Acid. — This  acid  was  investigated  by  Bourgoin.4 
In  a  concentrated  solution  of  sirupy  consistency  it,  like  oxalic 
acid,  is  only  slowly  oxidized  to  carbon  dioxide,  with  evolution 
of  oxygen.  A  strongly  concentrated  solution  of  the  unaltered 
acid  is  found  surrounding  the  positive  electrode,  even 'after  an 
electrolysis  of  long  duration.  On  electrolysis  of  the  sodium 
salt  carbon  monoxide  is  also  present  in  the  gaseous  mixture 
evolved.  The  proportions  of  the  various  gases,  carbon  mon- 
and  dioxide,  and  oxygen,  remain  fairly  constant  during  the 
period  of  electrolysis  (85.8%,  9.7%,  4.5%). 

In  alkaline  solution  the  decomposition  products  are  the 
same  as  in  neutral  splution,  only  the  proportions  of  the  individual 
gases  being  different,  and  varying  according  to  the  duration  of 
the  electrolysis. 

Miller,5  on  electrolyzing  malonates,  was  able  to  detect  a 
trifling  quantity  of  ethylene. 

Petersen  6  verified  this  fact.  He  formulated  the  following 
reactions : 


1  Ztschr.  f.  Elektrochemie  1,  90  (1894). 

2  Ztschr.  f.  anorg.  Chem.  31,  161  (1902). 
8  Ztschr.  f.  Elektrochemie  8,  897  (1902). 

*  Ann.  chim.  phys.  [1]  14,  157  (1857);  Bull.  d.  1.  soc.  chim.  33,  417  (1889). 
6  Journ.  f.  prakt.  Chemie  127,  328  (1879). 
6  Ztschr.  f.  phys.  Chemie  33,  700  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  107 

I.  CH2(COOH)2  =  CH2(COO)2  +  H2; 
II.  CH2(COO)2  +  H20  =  CH(COOH)2 

III.  2CH2(COO)2  =  C2 

IV.  CH2(COO)2  +  02- 


in  which,  however,  III  is  inconsiderable. 

The  Brown-  Walker  1  method  has  been  found  to  be  of  ex- 
cellent service  in  the  electrolysis  of  the  potassium  salts  of  the 
mono-esters  of  malonic  acid.  The  formation  of  the  diethyl 
ester  of  succinic  acid  from  ethyl  potassium  malonate  has  already 
been  mentioned  (p.  103). 

If  the  ethyl  potassium  salts  of  substituted  acids  are  chosen 
as  the  starting-point,  it  is  possible  to  obtain  disubstituted  acids, 
according  to  the  above  reactions. 

1.  Ethyl   potassium   methylmalonate    yields    the    two    sym- 
metrical dimethylsuccinic  acids  having  the  melting-points  193° 
and  121°. 

2.  Ethyl  potassium  ethylmalonate  yields  the  corresponding 
symmetrical  diethylsuccinic  acids,  with  the  melting-points  192° 
and    130°. 

3.  Ethyl    potassium    dimethylmalonate     affords    tetramethyl- 
succinic  acid. 

4.  From  ethyl  potassium  diethylmalonate  a  substance  having 
the  composition  Ci4H2604,  and  which  differs  from  the  expected 
tetraethyl-succinic  acid  by  C2H4,  was  obtained.    The  nature 
of  this  body  has  not  yet  been  determined. 

Hydrobromic  acid  splits  off  alcohol,  the  compound  Ci2H2003, 
which  has  perhaps  the  furfurane  formula 

(C2Hs)  2  '  C  —  C  :  (C2Hs)2  , 
0:C    C:0 


being  formed. 

All  these  reactions  do  not  take  place  smoothly,  but  are 
accompanied  by  secondary  reactions,   principally  oxidations, 


M.  c. 


108         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

which  are  limited  as  much  as  possible  by  working  with  strong 
concentrated  solutions  and  low  temperatures.  Moreover,  the 
formation  of  esters  also  is  always  possible  according  to  the 
equation 

2  CH3.COO  =  CH3COOCH3+C02; 

and,  finally,  the  formation  of  unsaturated  esters  may  take 
place  analogously  to  the  formation  of  ethylene  from  propionic 
acid: 

2  C2H5COO  =  C2H4  +  C02  +  C2H5COOH. 

Thus  it  was  possible  to  isolate  methylacrylic  add  by  the 
electrolysis  of  ethyl  potassium  dimethylmalonate: 


In  the  same  way  ethykrotonic  acid  is  formed  from  the  ethyl 
potassium  salt  of  diethylmalonic  acid. 

Mulliken,1  on  electrolyzing  sodium  malonic  diethyl  ester  in 
alcoholic  solution,  obtained  ethanetetracarboxylic  ester,  as  already 
mentioned.  Weems,2  on  electrolyzing  the  corresponding  com- 
pound of  methylmalonic  acid,  obtained  dimethylethanetetracar- 
boxylic  ester,  whereas  ethyljnalonic  ester  gave  diethylethanetetra- 
carboxylic  ester. 

The  method  of  von  Miller,3  electrolyzing  potassium  ethyl- 
malonate  with  potassium  salts  of  aliphatic  carboxylic  acids,  also 
gives  satisfactory  results.  If  potassium  acetate  is  chosen  as 
the  second  component  of  the  electrolytic  mixture,  propionic 
ethyl  ester  is  formed;  and  likewise  by  using  potassium  pro- 
pionate  or  potassium  butyrate  we  obtain  butyric  ethyl  ester  or 
valeric  ethyl  ester  respectively. 


1  Amer.  Chem.  Journ.  15,  323  (1893). 

2  Ibid.  16,  569  (1894). 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  28,  3438  (1895). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  109 

Nitromalonic  Acid. — According  to  Ulpiani  and  Gasparini,1 
a  hydro-alcoholic  solution  of  nitromalonic  ethyl  ester  does  not 
conduct  the  current,  but  an  aqueous  solution  of  the  ammonium 
salt  does.  According  to  this  the  ester  appears  as  a  true  nitro- 
compound: 

COOC2Il5 

CHN02    , 
COOC2H5 

but  its  ammonium  salt,  on  the  contrary,  as  an  isnitro-salt : 

COOC2H5 
C  =  NOONH4. 
COOC2H5 

The  electrolysis  of  this  latter  does  not  give  the  free  isonitro 
acid  at  the  anode,  but  the  dinitroethanetetracarboxylic  ester: 

COOC2H5 
2  CNOO      =  (COOC2H5)2C(N02)C(N02)(COOC2H5)2. 

COOC2Ii5 

The  ammonium  salt  of  nitromalonamide  yields  at  the  anode, 
only  free  nitromalonamide,  whereas  fulminuric  acid  (nitrocyan- 

acetamide),CN-CH(N02)-C/NH,  on  electrolysis  of  its  am- 
monium salt,  gives  a  new  reaction  product  which  has  not  yet 
been  investigated. 

Succinic  Acid. — Bourgoin  2  and  Kekule  3  found  that  the  free 
acid  underwent  oxidation  with  difficulty,  only  a  small  quantity 
of  carbon  monoxide  in  addition  to  some  oxygen  and  carbon 
dioxide  being  formed. 

The  neutral  sodium  salt  gave  the  same  products,  as  did  also 
the  alkaline  solution  of  this  salt,  except  that  in  the  latter  ex- 
periment the  formation  of  carbon  monoxide  predominated.  If, 
however,  four  molecular  equivalents  of  sodium  succinate  were 

1  Gazz.  chim.  32,  II,  235  (1902);   Ztschr.  f.  Elektrochemie  9,  477  (1903). 

2  Ann.  de  chim.  et  phys.  (4)  14,  157  (1866). 
3Lieb.  Ann.  131,84  (1864). 


110        ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

treated  with  one  equivalent  of  sodium  hydroxide,  ethylene  and 
a  little  acetylene  could  also  be  detected.  Kolbe  1  states  that 
methyl  oxide  is  also  formed;  Bourgoin,  however,  was  unable 
to  confirm  this  statement. 

Clarke  and  Smith,  2  on  oxidizing  succinic  acid  in  alkaline 
solution,  obtained,  besides  oxygen,  carbon  mon-  and  dioxide, 
ethylene,  methane,  tartaric  acid,  and  oxalic  acid. 

Petersen  3  was  unable  to  detect  either  carbon  monoxide  or 
acetylene  in  a  slightly  acid  electrolytic  solution  of  potassium 
succinate.  The  following  equations  essentially  express  the 
course  of  the  electrolysis: 


I.  C2H4(COOH)2  =  C2H4(COO)2 
II.  C2H4(COO)  2  +  H20  =  C2H4(COOH)2  +  0  ; 
III.  (C2H4)(COO)2  =  C2 


Small  variations  in  the  conditions  of  the  experiment,  as  well 
as  in  the  degree  of  acidity,  the  temperature,  and  the  kind  and 
size  of  the  electrodes,  exert  a  great  influence  on  the  course  of  the 
electrolysis. 

According  to  the  method  of  Brown  and  Walker,4  adipic 
diethyl  ester  is  formed  from  ethyl  potassium  succinate  : 

COOC2H5        COOC2H5 

I  I 

2(CH2)2       —(CH2)4.       +2C02. 

COO  COOC2H5 

Fairly  large  quantities  of  propionic  and  acrylic  esters  are 
also  formed,  probably  by  the  reaction 

2COOCH2CH2COOC2H5 

=  CH3  •  CH2COOC2H5+  CH2  :  CHCOOC2H5  +  2C02. 

1  Lieb.  Ann.  113,  244  (1860). 

2  Journ.  Amer.  Chem.  Soc.  21,  967  (1899). 
8  Ztschr.  f.  physik.  Chem.  33,  701  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  Ill 

Bouveault 1  claims  that  the  yield  of  adipic  acid  is  better  on 
electrolyzing  the  methyl  ester-salt  in  methyl-alcoholic  solution. 
He  obtained  a  yield  of  80%  by  using  a  mercury  cathode  and 
a  hollow  platinum  spiral  anode,  through  which  a  current  of  cold 
water  was  passed.  The  acid  succinic  methyl  ester  occurs  as  the 
principal  by-product,  also  a  neutral  methyl  ester  of  a  tribasic 
acid  which  was  not  investigated. 

Sodium  succinate  and  sodium  perchlorate,  electrolyzed  by 
Hofer  and  Moest,2  gave  hydracrylic  acid  as  the  chief  prod- 
uct, besides  acetaldehyde,  acetic  acid,  methyl  alcohol,  and 
formic  acid.  The  splitting  off  of  carbonic  acid  and  the  intro- 
duction of  the  hydroxyl  group  occurs  only  at  one  carboxyl 
group: 

CH2-COO  CH2-OH 

CH2-COOH  +OH=  I  +C02. 

CH2-COOH 

Von  Miller  and  Hofer  3  have  also  carried  out  the  principle 
of  the  electrolysis  of  mixtures,  discussed  under  malonic  acid, 
using  potassium  ethyl  succinate,  and  submitting  the  latter  to 
electrolysis  at  the  anode  with  potassium  salts  of  monocarboxylic 
acids.  They  thus  obtained  on  the  addition  of  potassium  acetate 
about  69%  of  the  theoretical  quantity  of  butyric  ethyl  ester : 

CH3  •  COO  +  COO  •  CH2  •  CH2  •  COOC2H5 

=  CH3  •  CH2  •  CH2  -  COOC2H5 + 2C02 . 

Incidentally  a  yield  of  about  22%  of  adipic  ester  was  ob- 
tained. 

The  synthesis  of  valeric  ethyl  ester  from  potassium  ethyl 
succinate  and  sodium  propionate  was  accomplished  in  the  same 
way: 

CH3  •  CH2  •  COO  +  COO(CH2)2COOC2H5 

=  CH3(CH2)3COOC2H5  +  2C02. 

,..     .»  Bull.  soc.  chim.  29,  1038,  1043  (1903). 
2Lieb.  Ann.  323,  284  (1902). 
3  Ber.  d.  deutsch.  chem.  Gesellsch.  28,  2431  (1895). 


112         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Furthermore,  by  using  a  mixture  of  potassium  ethyl  succinate 
and  potassium  isobutyrate,  isobutylacetic  ester  was  obtained  : 

(CH3)2  :CHCOO+COO(CH2)2COOC2H5 

=  (CH3)2:CH(CH2)2COOC2H5+2C02. 

Vanzetti  and  Coppadoro  1  have  extended  the  von  Miller- 
Hofer  method  to  the  electrolysis  of  a  mixture  of  ethyl  potassium 
malonate  and  ethyl  potassium  succinate.  They  obtained  a  poor 
yield  of  the  desired  glutaric  diethyl  ester: 


COOC2H5  •  CH?  .  COO  +  COO  •  CH2  •  CH2  •  COOC2H5 

=  COOC2H5  •  CH2  •  CH2  •  CH2  •  COOC2H5  +  2C02. 

Moreover,  succinic  diethyl  ester  was  formed  from  the  malonic 
acid,  and  adipic  diethyl  ester  from  the  succinic  acid. 

Pyrotartaric  Acids 

Glutaric  Acid  (Normal  Pyrotartaric  Acid).  —  The  results  ob- 
tained by  Reboul  and  Bourgoin  2  are  the  f  oil  owing  :  A  large 
part  of  the  acid  remains  unchanged,  while  a  small  part  is 
decomposed  according  to  the  following  equation: 

02C02  +  3CO  +  4H20. 


2v 
A  hydrocarbon  of   the  composition  I        /CH2  was  not  ob- 

CH/ 
tained;  nor  was  an  olefine  formed. 

Similar  observations  were  made  in  the  electrolysis  of  potas- 
sium glutarate,  also  in  alkaline  solution. 

Petersen3  expresses  the  course  of  the  electrolysis  by  the 
following  equations: 

1  Atti  R.  Accad.  dei  Lincei  12,  II,  209  (1,903). 

2  Bull.  soc.  chim.  27,  545  (1877)  ;  Compt.  rend.  84,  1231,  1395  (1877). 

3  Ztschr.  f.  phys.  chem.  33,  703  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  113 


I.  (CH2)3(COOH)2  =  (CH2)3(COO)2 
II.  (CH2)3(COO)2  +  H20  =  (CH2)3(COOH)2  +  0;     . 
III.  (CH2)  3  (COO)  2  +  3  02  =  2C02  +  SCO  +  3H20. 

The  expected  reaction, 

(CH2)3(COO)2  =  (CH2)3  +  202, 

does  not  take  place. 

Brown  and  Walker  l  obtained  the  diethyl  ester  of  suberic 
acid  from  ethyl  potassium  glut  ar  ate. 

Pyrotartaric  Acid  (Methylsuccinic  Acid).  —  Reboul  and  Bour- 
goin,2  on  electrolyzing  a  solution  of  the  neutral  potassium  salt, 
obtained  a  deposit  of  the  acid  salt  ;  the  formation  of  such  an  acid 
salt  in  the  case  of  glutaric  acid  does  not  occur.  On  continued 
electrolysis  the  crystals  disappear,  the  free  acid  being  regener- 
ated. In  alkaline  solution,  also,  the  formation  of  the  acid  salt 
occurs  on  prolonged  electrolysis.  Nevertheless  the  continuous, 
though  slight,  evolution  of  carbon  dioxide  and  carbon  mon- 
oxide is  a  proof  of  extensive  oxidation. 

Petersen,3  on  electrolyzing  a  20%    solution   of   potassium 
pyrotartrato,  found  propylene,  besides  carbon  mon-  and  dioxide 
among  the  evolved  gases: 

CH3  CH3 

CHCOO  =  CH  +2C02. 
CH2COO    CH2 

Primary  and  secondary  propyl  alcohol  could  be  isolated  from 
the  electrolyzed  fluid,  both  of  which  seemed  to  be  formed 
from  propylene  by  addition  of  water  : 

I.  CH3  CH3 

CH  +OH=CHOH 
CH2    H 


II.  CH3  CH3 

CH  +  H    =CH2 
CH2    OH    CH2OH. 

M.  c.  '  1.  c.  3  1.  c. 


114         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  strong  aldehyde  reaction  of  the  electrolyte,  after  the 
experiment  was  finished,  indicates  that  the  primary  alcohol 
is  partially  oxidized  further  to  propionic  aldehyde,  or  that 
the  propylene  can  yield  propylene  ox  de  through  the  influence 
of  the  anodic  oxygen,  and,  by  molecular  rearrangement,  the 
a  dehyde: 

CH3          CH3  CH3 


CH  +0  =  CH\     =CH2 
CH2          CH2/       COH. 

Ethylmalonic  Acid.  —  The  behavior  of  ethyl  potassium 
ethylmalonate  has  already  been  mentioned  in  the  discussion 
of  malonic  acid.  The  potassium  salt,  in  a  20%  slightly  acid 
solution,  yields  propylene  (Peter  sen  0,  and  probably,  like  pyro- 
tartaric  acid,  primary  and  secondary  propyl  alcohol. 

Adipic  Acid.  —  The  ethyl  potassium  salt  was  converted  into 
the  sebacic  diethyl  ester  by  Brown  and  Walker  1  : 

COOC2H5     COOC2H5 

2(CH2)4       =(CH2)8       +2C02. 
COO  C"OOC2H6 

Pimelic  Acid.  —  In  the  same  manner,  the  diethyl  ester  of 
n-decanedicarboxylic  acid  is  formed  from  the  ester  potassium 
salt  of  pimelic  acid  (Komppa,2  also  Walker  and  Lumsden3). 
n-Pentenecarboxylic  ethyl  ester  occurs  as  a  by-product  at  the 
anode  : 

I.    COOC2H5     COOC2H5 
2(CH2)5       =  (CH2)io      +2C02; 
CO  COOC2H5 

II.    COOC2H5     COOC2H5      COOC2H5 

2(CH2)5       =  (CH2)3      +   (CH2)5      +C02. 
COO  CH  COOH 

CH2 

M.  c. 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  900  (1901). 

3  Journ.  Chem.  Soc.  79,  1197  (1901). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  H5 

Suberic  Acid,  by  the  same  method,  gives  the  ester  of  n-do- 
decanedicarboxylic  acid,  likewise 

Sebacic  Acid,  the  ester  of  n-decahexanedicarboxylic  acid 
(octodecandi-acid),  besides  sebacic  diethyl  ester  and  the  ester 
of  the  unsaturated  acid  CH2:CH(CH2)6COOH. 

The  decompositions  which  the  acids  (or  their  potassium 
salts)  of  the  oxalic  -acid  series  undergo  can  be  essentially  inter- 
preted by  the  following  equations  : 


II.  CnH 
III.  CnH2n(COO)2 

IV.  Unsaturated  Dibasic  Acids. 

Maleic  Acid.  —  According  to  the  investigations  of  Kekule,1 
a  concentrated  solution  of  the  sodium  salt  gives,  on  electrolysis, 
acetylene,  and  also  carbon  dioxide  at  the  anode,  while  a  little 
succinic  acid  is  formed  at  the  cathode.  A  molecular  rear- 
rangement to  fumaric  acid  also  occurs  to  a  trifling  extent. 
Brommalelc  acid  decomposes  into  hydrobromic  acid,  and  carbon 
mon-  and  dioxides. 

Ethyl  Potassium  Maleate  does  not  react  conformably  to  the 
reaction  of  Brown  and  Walker  (Shields2),  but  gives,  in  concen- 
trated solution,  carbonic  acid,  oxygen,  and  unsaturated 
hydrocarbons;  however,  much  of  the  material  serving  for  the 
starting-point  remains  unchanged. 

Fumaric  Acid.  —  This  acid  was  also  investigated  by  Kekule. 
At  the  beginning  of  the  experiment  it  gives  pure  acetylene  and 
carbon  dioxide,  but  after  the  operation  has  continued  for  some 
tune  the  acetylene  was  found  to  be  mixed  with  oxygen.  Ethyl 
potassium  fumarate  behaves  exactly  like  the  maleate. 

Itaconic  Acid.  —  The  concentrated  solution  of  the  alkali  salt, 
electrolyzed  by  Aarland,3  gave  a  hydrocarbon  isomeric  with 
allylene,  CaKU,  which  is  said  to  have  the  formula  CH2  =  C  =  CH2; 

1  Lieb.  Ann.  131,  85  (1864). 

2  Ibid.  274,64  (1893). 

3  Journ.  prakt.  Chem.  [2]  4,  376  (1871),  [2]  6,  256  (1872). 


116         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

along  with  this  compound,  some  propylene  was  formed,  while 
a  portion  of  the  acid  was  always  regenerated. 

Citraconic  Acid. — The  concentrated  solution  of  the  sodium 
salt,  likewise  electrolyzed  by  Aarland,1  yielded,  besides  a  hydro- 
carbon, C3H4,  small  traces  of  acrylic  and  mesaconic  acids. 

Mesaconic  Acid,  under  similar  conditions,  gives  the  same 
hydrocarbon  and  traces  of  acrylic  and  ita^conic  acids. 

The  unsaturated  acids,  on  electrolysis,  consequently  appear 
to  give  no  synthetic  products  at  all.  The  aromatic  acids,  like 
phthalic  and  benzylmalonic  acid,  behave  similarly. 

V.  Polybasic  Acids. 

Malic  Acid. — The  electrolysis  of  malic  acid  was  effected  by 
Bourgoin  2  and  Brester.3  Both  the  free  acid,  which  is  but  slowly 
decomposed,  and  the  neutral  alkali  salt,  gave  the  same  products, 
carbon  dioxide  and  a  little  carbon  monoxide  and  oxygen. 
After  the  completion  of  the  experiment  the  solution  contained 
some  aldehyde  and  acetic  acid.  Von  Miller  and  Hofer  4  also 
found  crotonaldehyde. 

Tartaric  Acid  (Dextro-rotary). — The  free  acid  is  partially 
oxidized  (Bourgoin 5  and  Kekule 6)  to  carbon  dioxide  and 
carbon  monoxide,  while  the  solution  contains  acetic  acid. 
Neutral  potassium  tartrate  gives  principally  carbon  dioxide 
besides  a  little  carbon  monoxide  arid  oxygen,  acid  potassium 
tartrate  being  at  the  same  time  deposited.  In  alkaline  solutions 
the  same  gases  carry  with  them  traces  of  ethane,  the  formation 
of  which  is  due  to  potassium  acetate,  which  is  found  present  in 
the  solution  at  the  end  of  the  operation;  also  some  ethylene. 
Von  Miller  and  Hofer  7  obtained  from  a  concentrated  solution 
of  potassium  tartrate  carbon  mon-  and  dioxides  and  oxygen, 

1  Journ.  prakt.  Chem.  [2]  7,  142  (1873). 

2  Bull.  soe.  chim.  [2]  9,  427  (1868). 

3  Ibid.  8,  23  (1867). 

4  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  470  (1894). 

8  Compt.  rend.  65,  1144  (1867);  Bull.  soc.  chim.  [2]  11,  405  (1869). 

6  Lieb.  Ann.  131,  88  (1864). 

7  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  470  (1894). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  117 

with  a  little  formaldehyde  and  formic  acid,  but  no  acetic  acid 
and  ethylene  as  affirmed  by  Bourgoin.  The  ethyl  ester  behaves 
in  a  like  manner. 

Racemic  Acid.  —  The  same  investigators  found  that  racemic 
acid,  on  electrolysis  of  the  sodium  salt  in  aqueous  solution, 
gives  carbon  mon-  and  dioxides  and  an  aldehyde  which  was 
not  further  investigated. 

Ethyltartaric  Acid.  —  This  gave  the  same  gases,  but  any 
other  substances  which  may  have  been  formed  were  not  identi- 
fied. 

Methanetricarboxylic  Acid.  —  Mulliken1  employed  the  method, 
which  has  already  been  discussed  (p.  104),  in  the  electrolysis 
of  the  sodium  salt  of  the  triethyl  ester  of  this  acid  and  ob- 
tained ethanehexacarboxylic  ester,  besides  some  malonic  ester. 
Further  oxidation  caused  the  formation  of  sodium  bicarbonate: 


Tricarballylic  Acid.  —  The  potassium  salt  of  the  diester  of 
this  acid  was  subjected  by  von  Miller2  to  the  Brown-  Walker 
reaction,  but  without  success.  The  ester-acid  was  in  part 
regenerated.  When  potassium  acetate,  however,  was  added  to 
the  anode  solution  the  expected  reaction  occurred;  ethylsuc- 
cinic  ester  was  produced: 

CH2  COOC2H5 


I  COOC2H5 

CH2.COO 

The  peculiar  fact  that  the  di-esters  of  tricar  bally  lie  acid,  when 
electrolyzed  by  themselves,  do  not  afford  the  expected  synthet- 
ical reaction,  while  the  electrolysis  of  a  mixture  of  the  acid 
with  potassium  acetate  gives  these  synthetic  products,  was 
made  use  of  by  von  Miller  with  several  aromatic  acids  which 
had  previously  proven  unsuitable  for  synthesis  when  used  alone 
(see  these). 


1  Am.  Chem.  Journ.  15,  323  (1893) 

2  Ztsch.  f.  Elektrochemie  4,  55  (1897). 


118         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Aconitic  Acid. — On  electrolyzing  a  concentrated,  strongly 
alkaline  solution  of  the  potassium  salt,  Berthelot 1  observed 
oxygen,  carbon  monoxide,  and  a  little  acetylene  at  the  anode. 

Marie  2  was  able  to  convert  aconitic  acid  into  tricarballylic 
acid  at  a  mercury  cathode  surrounded  with  a  solution  of  the  acid 
half  neutralized  with  sodium  hydrate.  Sixty  per  cent  of  the 
theoretical  yield  was  obtained : 

CH-COOH  CH2-COOH 

C  •  COOH     + 2H = CH  •  COOH 
CH2-COOH  CH2-COOH. 

7.  AMINES,  ACID  AMIDES,  IMIDES,  AND  NITRILES. 

The  literature  on  these  subjects  is  very  scarce.  Little  is 
known  regarding  the  electrolysis  of  amines,  whose  anodic 
behavior  would  probably  be  very  interesting.  They  are  stable 
at  the  cathode,  and  can  be  obtained  electrolytically  by  reduction 
of  the  nitriles.  Weems  3  has  electrolyzed  acid  amides  in  the  form 
of  their  sodium  or  mercury  compounds.  He  obtained  only  the 
unchanged  material  used  as  the  starting-point. 

Tetramethylammonium  Hydrate. — Palmaer  4  electrolyzed  a 
solution  of  the  hydrate  in  liquid  ammonia  in  a  Dewar  vessel 
at  about  —  41°.  Deep-blue  rings  having  the  color  of  a  solution 
of  sodium  in  liquid  ammonia  appeared  at  the  cathode  when  the 
circuit  was  closed.  A  solution  of  free  tetramethylammonium 
is  probably  formed,  which  could  not  be  isolated.  The  chloride 
behaves  like  tetramethylammonium  hydrate. 

Tetraethylammonium  Chloride. — Goecke  5  has  investigated 
the  behavior  of  the  iodide  of  this  compound  in  aqueous  solution. 
He  found  at  the  anode  tetraethylammonium  triiodide : 

N(C2H5)4M2. 

1  Compare'  Bourgoin,  Bull.  soc.  chim.  [2]  9,  103  (1868). 

2  Compt.  rend.  136,  1331  (1903). 

3  Am.  Chem.  Journ.  16,  569  (1894). 

4  Ztschr.  f.  Elektrochem.  8,  729  (1902). 
elbid.  10,250  (1904). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  119 

The  yield  was  40%  of  the  material  used  as  the  starting-point. 
A  little  iodoform  is  also  produced,  by  the  action  of  iodine  on 
portions  of  the  original  iodide  destroyed  by  oxidation. 

The  method  of  Tafel  (p.  23),  which  has  been  discussed  in 
the  theoretical  part,  has  also  done  good  service  in  the  reduction 
of  succinimide  and  some  of  its  derivatives.  This  method,  — 
for  reducing  in  sulphuric-acid  solution  substances  reducible  with 
difficulty,  —  has  also  proven  very  fruitful  in  the  domain  of  the 
carbonic-acid  derivatives  and  of  the  alkaloids. 

Succinimide.  —  Tafel  and  Stern,1  by  reduction  of  this  sub- 
stance in  a  50%  sulphuric  acid,  obtained  about  60%  of  a  yield 
of  pyrrolidone.  The  fluid  was  kept  cold  and  electrolyzed  at 
high  current  densities: 

CH2-COX  CH2-CH2V 

>NH  +  H2  =  >NH. 

CH2-C(X  -/ 


Fairly  large  quantities  of  substances  having  higher  boiling- 
points,  but  which  do  not  boil  without  decomposition,  are  also 
produced. 

The  reduction  of 

Isopropylsuccinimide,  likewise  electrolyzed,  gave  a  yield  of 
about  80%  of  the  theoretical  of  isopropylpyrrolidone  : 


CH2-C(\ 

|  >N-CH(CH3)2  +  H2  =    |  >N-CH(CH3)2. 

CHa-CCK  CH2.CO  / 


Succinanil  was  converted  by  the  same  method  (Baillie  and 
Thomas2),  but  in  concentrated  sulphuric  acid,  into  phenylpyr- 
rolidone  : 

CH2-CO\  CH2-CH2X 

>NC6H5  +  H2  =   ,  NC6H5. 

CHa-CCK 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  33,  2224  (1900). 

2  Ibid.  32,   68  (1899). 


120         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

A  moderate  yield  of  p-tolylpyrrolidone  is  obtained  from 
p-tolylsuccinimide  in  95-%  sulphuric  acid: 


CIl2  *  C0\ 

>N  •  C6H4  •  CH3  +  H2  =  >NC6H4  •  CH3. 

CH2-CCK  CH2-CO  / 

Acetylpyrrolidone  can  be  reduced  to  ethylpyrrolidone  in  a 
50%  sulphuric  acid  (Tafel  and  Stern  x)  : 


2\ 

NCOCH3  +  2H2  =  >NC2H5+H20. 

CH2-CO  '  CH2-CO  > 

Hydrocyanic  Acid.  —  In  sulphuric-acid  solution  hydrocyanic 
acid  breaks  up  smoothly,  according  to  Gay-Xussac,2  into  hydro- 
gen and  cyanogen.  Concentrated  hydrocyanic  acid  to  which  a 
drop  of  sulphuric  acid  has  been  added  gives  carbon  monoxide 
and  ammonia  (Schlagdenhauffen  3)  . 

Potassium  Cyanide.  —  In  the  investigation  of  this  salt,  con- 
ducted by  the  author  last  mentioned,  it  was  found  that  no 
oxygen  escaped  at  the  anode,  but  the  potassium  cyanide  was 
oxidized  to  potassium  cyanate.  Bartoli  and  Papasogli  obtained 
mellogene  from  potassium  cyanide  by  using  carbon  anodes, 
and  mellitic  acid  at  graphite  anodes. 

Potassium  Ferrocyanide.  —  This  compound  gives  at  the 
anode  hydrocyanic  acid  and  Prussian  blue,  and  at  the  cathode 
hydrogen  and  potassium  hydroxide  (Perrot4);  also  cyanogen 
(Schlagdenhauffen5  and  Schonbein). 

Potassium  Ferricyanide  on  electrolysis  likewise  gives  Prus- 
sian blue  6  at  the  anode,  being  the  first  electrolytic  oxidation 
product  of  potassium  ferrocyanide. 

Sodium  Nitroprusside.  —  On  electrolyzing  a  dilute  solution  of 
this  salt  for  a  prolonged  period,  Weith  7  noted  the  formation  of 

U.  c. 

2  Am.  chim,  phys.  78,  245  (1811). 

3  Jahresb.  f.  Chem.  1863,  305. 

4  Tommasi,  Traite"  d'Electrochimie  720. 

6  Journ.  f.  prakt.  chemie  30,  145  (1843). 

6Eng.  Pat.  No.  7426  (1886);  Elect.  Review  32,  216  (1893). 

7  Jahresb.  f.  Chem.  1863,  306,  1868,  311. 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  121 

ammonia  and  precipitation  of  metallic  iron;  at  the  positive 
electrode  Prussian  blue  appeared,  and  nitrogen,  oxygen,  and, 
if  the  operation  was  long  continued,  nitric  oxide,  also,  were  given 
off.  In  a  concentrated  solution  much  ammonia  was  formed  at 
the  cathode,  and  nitric  oxide  appeared  at  the  anode. 

Nitriles.  —  Ahrens,1  by  means  of  the  electrolytic  addition  of 
hydrogen,  succeeded  in  converting  nitriles  into  primary  amines, 
while  simultaneously  with  the  reduction  a  partial  saponification 
of  the  nitriles  occurred,  as  represented  by  the  following  equation  : 

R.CN  +  2H20  =  R.COOH  +  NH3. 

Acetonitrile.  —  This  substance  in  sulphuric  -  acid  solution 
yields  only  a  small  quantity  of  ethylamine,  although  a  con- 
siderable quantity  of  n-propylamine  is  formed  from  n-propyl- 
nitrile. 

The  reduction  of  aromatic  nitriles  takes  place  without  the 
occurrence  of  secondary  reactions.  This  is  illustrated  in  the 
formation  of  benzylamine  from  benzonitrile  and  of  phenyl- 
ethylamine  from  benzylcyanide. 

8.  CARBONIC  ACID  DERIVATIVES. 

Tafel  and  his  school  have  investigated  the  uric-acid  group, 
which  includes  the  ureides  of  dibasic  acids,  as  to  its  behavior 
when  electrolytically  reduced  at  lead  cathodes  in  sulphuric-acid 
solution.  All  members  of  this  group  belong  to  the  difficultly 
reducible  substances;  the  electrolytical  effect  can  often  not  be 
attained  by  chemical  means.  The  reduction  ,does  not  affect  the 
urea-group,  but  does  act  on  the  ketone-groups  and  the  double 
bonds  of  the  radicals  united  with  the  carbamide-molecule.  Thus 
parabanic  acid  is  converted  into  hydantoin  and  ethylene-urea  ; 

/NH-CO  XNH-CH2 

1.  C0<  |     +2H2=CO<  |       +H20; 

XNH-CO  XNH-CO 

.NH-CO  XNH-CH2 

2.  C0<  |    +4H2  =  CO<  |      +2H20. 

CO  XNH-CH2 


Ztsch.  f.  Electrochemie  3,  99  (1896). 


122         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS 

E.  Fischer  claims  that  the  members  of  the  uric-acid  group 
can  be  considered  as  derived  from  purin,  a  parent  substance : 

(6) 

(1)  N  =  CH; 

I  I       (7) 

(2)  CH(5)C-NHX 

II  II  >H. 

(3)  N  -  C-N    ^(8) 

(4)  (9) 

Accordingly,  uric  acid  appears  as  2,  6,  8-trioxypurin,  and 
caffeine  as  1,  3,  7-trimethyl-2;  6-dioxypurin : 

HN-CO  CH3N-CO 

II  I      I     CH3 

CO  C-NHX  CO  C-N 


>CO;  |      ||        >CH. 

HN-C-NH/  CH3N-C-N^ 

Uric  acid  Caffeine 

In  the  electrolytical  reduction  of  the  investigated  purin 
derivatives,  it  appeared  that  the  oxygen  in  position  (6)  of  the 
purin  nucleus  is  the  only  one  that  can  be  eliminated  for 
hydrogen.  But  an  addition  of  hydrogen  occurs  also  without  a 
loss  of  oxygen;  this  happens  in  the  conversion  of  uric  acid  into 
tetrahydrouric  acid.  Further  particulars  will  be  mentioned 
under  the  individual  substances. 

Parabanic  Acid,  the  ure'ide  of  oxalic  acid  and  oxidation 
product  of  uric  acid  obtained  by  the  action  of  nitric  acid,  is 
converted  into  hydantoin  and  ethyl  urea  (Tafel  and  Reindl x). 

Methyluracyl,  the  reaction  product  of  acetoacetic  ester  and 
urea  (water  and  alcohol  being  eliminated),  can  be  easily  reduced 
in  sulphuric-acid  solution  (Tafel  and  Weinschenk2).  Methyl- 
trimethylene  urea  is  formed,  also  a  considerable  quantity  of  1.3- 
diaminobutane : 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  3286  (1901), 

2  Ibid.  33,  3378  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  123 

NH-C-CH3  NH-CH-CH3 

I  II  II 

I.  CO     CH        +3H2  =  CO     CH2         +H20; 

II  II 
NH-CO                     NH-CH2 

NH  -  CH  -  CH3  NH2  -  CH  •  CH3 

I          I  I 

II.  CO     CH2        +H20=  CH2        +002. 

NH-CH2  NH2-CH2 

Barbituric  Acid,  Malonyl  Urea,  was  investigated  by  the 
same  authors.  It  likewise  gives  two  products,  hydrouracyl 
and  trimethylene  urea: 

NH-CO  NH-CH2 

II  II 

I.  CO     CH2+2H2  =  CO     CH2  +  H20; 

II  II 

NH-CO  NH-CO 

NH-CO  NH-CH2 

||  || 

II.  CO     CH2+4H2  =  CO     CH2  +  2H20. 

II  II 

NH-CO  NH-CH2 

The  convertibility  of  maionyl  urea  into  trifiiethylene  urea 
taken  in  connection  with  the  decomposability  of  the  cyclical  ureas 
into  cliamines  and  carbonic  acid  affords  a  simple  method  of 
obtaining  1.3-diaminopropane  from  malonie  acid  in  the  same 
manner  as  1.3-diaminobutane  is  produced  from  methyl  uracyl: 

NH-CH2  NH2-CH2 

CO     CH2  +  H20=  GH2+C02. 

NH-CH2  NH2-CH2 

Dialuric  Acid,  Tartronyl  Urea. — Tafel  and  Reindl 1  reduced 
this  substance  and  obtained  as  chief  reduction  product  hydro- 
uracyl, also  some  trimethylene  urea  and  oxytrimethylene  urea: 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  33,  3383  (1900). 


124         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

NH-CO  NH-CH2 

II  II 

I.  CO     CHOH+3H2  =  CO     CH2  +  2H20; 

I         I  I 

NH-CO  NH-CO 

NH-CO  NH-CH2 

II.  CO     CHOH  +  5H2  =  CO     CH2-f3H20; 

I  I       'I 

NH-CO  NH-CH2 

NH-CO  NH-CH2 

I         I  I 

III.  CO     CHOH+4H2  =  CO     CHOH  +  2H20. 

NH-CO  NH-CH2 

Uramil  is  the  reduction  product  of  violuric  acid,  which  is 
the  isonitroso-compound  of  barbituric  acid: 

NH-CO 

I         I 
CO     CH-NH2. 

NH-CO 

It  is  easily  reducible,  ammonia  being  split  off,  and  forms  hydro- 
uracyl  1  as  the  solely  crystallizable  body.  The  same  product  is  de- 
rived in  considerable  quantity  in  the  electrolytic  reduction  of 
Alloxan,  Mesoxalyl  Urea.  There  are  also  produced  in  this 
reduction  alloxantin,  which  is  difficulty  soluble  and  can  only 
slowly  be  reduced  further,  and  large  quantities  of  non-crystal- 
lizable  gummy  substances: 

NH-CO  NH-CH2 

II  II 

I.    CO     CO+4H2=CO    CH2+2H20; 

II  II 

NH-CO  NH-CO 

NH-CO  NH-CO  CO-NH 

I        I  I  /0\J        I 

II.  2CO     CO  +  H2  =  CO     C  /—  XC       C0  +  H20. 


NH-CO  NH-CO  CO-NH 

Alloxantin 


Ber.  d.  deutsch.  chem.  Gesellsch.  34,  3290  (1901). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  125 

Uric  Acid. — The  reduction  of  uric  acid  can  be  conducted  in 
such  a  way  that  it  takes  place  principally  according  to  the  fol- 
lowing equation  (Tafel *) : 

C5H403N4 + 6H  =  C5H802N4  +  H20. 

Tafel  calls  the  resulting  product  puron,  and  gives  it  the 
following  formula: 

NH-CH2 


CO     CH-NH\ 

I         I  >0. 

NH-CH-NH/ 

It  is  formed  almost  exclusively  in  the  reduction  of  uric  acid 
in  a  75%  sulphuric  acid  at  5°-8°  and  with  high  current  con- 
centration. A  part  of  the  puron  is  molecularly  rearranged 
already  at  12°- 15°,  forming  an  isomeric  substance,  isopuron. 
The  structure  of  the  latter  has  not  yet  been  explained.  Tetra- 
hydrouric  acid  and  isopuron  are  formed  in  80%  sulphuric  acid 
at  20°  and  with  a  lower  current  concentration. 

The  reactions  can  be  expressed  by  the  following  equations: 
NH-CO  NH-CH2 

II  II 

I.  CO     C-NHV  CO     CH-NH 


.v  \J\J          \JLL  —  1>  A1X 

>CO+3H2=|         |  >CO  +  H20; 

/  NTT-nTT-NU/ 


NH-C-NH/  NH-CH-NH^ 

Uric  acid  Puron 

NH-CO 

I 
II.  CO     C-NHX 

|          ||  >CO+2H2 

NH-C-NHX 

NH  -  CH2  NH2CONH  •  CH2 

I  I  I 

=  CO     CH-NHCONH2  CH-NH\ 

II  or  |  \X). 
NH-CO                                          CO-NH/ 


Tetrahydrouric  acid 


Ber.  d.  deutsch.  chem.  Gesellsch.  34,  258  (1901). 


126         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  structure  of  the  last-mentioned  acid  has  not  yet  been 
determined  with  certainty.1 

Strange  to  state,  the  methylated  uric  acids,  when  reduced, 
do  yield  purons  which  (excepting  tetramethylpuron)  can  be 
molecularly  rearranged  into  isomeric  isopurons,  but  the  corre- 
sponding hydrated  uric  acids  are  not  produced  (Tafel  2)  . 

3-Methyluric  Acids.  —  The  two  isomeric  and  structurally 
identical  3-methyluric  acids,  the  d-  and  £-acids,  give  3-methyl- 
purons.  These  latter  are  extremely  similar,  but  show  differ- 
ences in  solubility  which  point  to  the  possibility  of  an  isomerism. 
A  certain  quantity  of  isopurons  was  already  formed  during 
electrolysis  by  the  rearranging  action  of  the  60-70%  sulphuric 
acid  used  as  electrolyte:  .  . 

NH-CO  NH-CH2 

II  II 

CO      C-NHX  CO    CH-NHX 

|         ||  >CO+3H2  =        |         |  >CO  +  H20. 

CH3N  -  C-NH/  CH3N  -  CH-NH/ 

1.3-Dimethyluric  Acid.  —  The  reduction  to  1.3-dimethyl- 
puron  takes  place  very  slowly  in  a  75%  sulphuric  acid  solution. 
The  molecular  rearrangement  to  isopuron  is  also  very  slow. 

3.9-Dimethyluric  Acid  gives  similarly  a  3.9-dimethylpuron 
which,  if  heated  in  a  10%  sodium-hydrate  solution,  smoothly 
rearranges  itself  to  form  the  iso-compound.  The  electrolytical 
effect  is  hence  a  normal  one  i- 

NH-CO  NH-CH2 

II  II 

CO     C    -NHV  CO     CH-NHX 

|         ||  >CO+3H2=      |         |  >CO+H20. 

CH3N    -C    -N    /  N    -CH-N   / 


7.9-Dimethyluric  Acid  gives  correspondingly  a  7.9-dimethyl- 
puron. 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  1181  (1901). 

2  Ibid.,  279  (1901). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  127 

i.3.7-Trimethyluric  Acid,  or  Hydroxycaffeine,  is  changed 
into  1.3.7-trimethylpuron  by  electrolytic  reduction  in  60% 
sulphuric  acid.  A  good  yield  is  obtained.  By  hydrochloric 
acid,  and  also  by  heating  in  a  10%  sodium-hydroxide  solution, 
it  is  converted  into  the  trimethylisopuron. 

Tetramethyluric  Acid.  —  This  substance,  by  reduction  in 
50%  sulphuric  acid,  is  changed  to  tetramethylpuron.  The 
latter  does  not  rearrange  itself. 

CH3N  -CO  CH3N  -CH2 

I        |        CH3  ||        CH3. 

CO    C    -Nv  CO    CH-Nv 

||  >CO+3H2=  |  >CO  +  H20 

CH3N   -C    -N/  CH3N   -CH-NX 

CH3  CH3 

Tafel  has  proposed  the  following  three  formulas  for  isopuron: 

N      -CH2  N      -CH2 

II  I  II  I 

COH    CH-    N^  COH     CH-NHV 

I  I  >OH  |  |  >CO. 

NH    -CH-NH/  NH    -CH-NH/ 

I.  II. 

N     — CH2 


H    CH-NH, 
I  I  >COH. 

NH  -CH-    W 
III. 

Tafel  has  also  successfully  reduced  the  xanthine  bases: 
Guanine,  xanthine,  theobromine,  caffeine,  adenine  and  hypo- 
xanthine,  or  sarcine.  The  electrolyte  was  a  sulphuric-acid 
solution,  and  lead  cathodes  were  employed. 

The  effect  consists  in  the  addition  of  two  hydrogen  atoms 
and  the  elimination  of  an  atom  of  oxygen.  Tafel  calls  the 
reduction  products  desoxy-bodies.  Their  formation  is  char- 
acteristic of  the  xanthine  bases. 

Xanthine,  on  reduction  in  75%  sulphuric  acid,  yields 
desoxyxanthine.  The  yield  is  70%  of  the  theoretically  possible 


128         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

quantity.    The  reaction  takes  place  in  accordance  with  the  fol- 
lowing equation: 

NH-CO  NH-CH2 

II  I      i 

CO     C-NHX  CO     C-NHV 

I  II  \r<TT_LOTT  I  II  \PTTj_TT  r* 

>U±  +  2H2=  |  X,H  +  H2U. 

NH-C-     W  NH-C-    N^ 

Xanthine  Desoxyxanthine 

The  latter  compound  is  therefore  to  be  regarded  as  2-oxy- 
1.6-dihydropurin.  These  experiments  were  made  by  Tafel 
and  Ach.1 

3-Methylxanthine  gives  analogously  3-methyldesoxyxan- 
thine  or  3-methyl-2-oxy-1.6-dihydropurin  (Tafel  and  Wein- 
schenk2),  and 

Heteroxanthine,  7-Methylxanthine,  yields  desoxyhetero- 
xan thine,  or  7-methyl-2-oxy-1.6-dihydropurin: 

NH-CO  NH-CH2 

II  II 

I.  CO     C-NHX  CO     C-NH\ 

|         ||  >CH+2H2=        |         || 

CH3N    -C-    W  CH3N    -C-N 

NH-CO  NH-CH2 

I         |     CH3.  ||     CH3 

II.  CO     C-N\  CO  -C-N 


NH-C-N  NH-C-N 

If  desoxy-compounds  are  suitably  oxidized,  they  lose  two 
atoms  of  hydrogen  and  pass  into  oxypurins.  3-Methyldes- 
oxyxanthine  is  thus  converted  into  3-methyl-2-oxypurin : 


COC-NHX 
I      II  >H, 

CH3N-C-    N^ 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  1165  (1901). 

2  Ibid.  33,  3369  (1900). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  129 

and  desoxyheteroxanthine  gives  the  corresponding  7-methyl- 
2-oxypurin.  These  oxidation  products  furnish  the  proof  of 
the  constitution  of  desoxy-compounds.  The  constitution  for 
some  of  the  members  had  been  determined  by  E.  Fischer  through 
synthesis. 

Theobromine,  or  3.7-Dimethylxanthine,  was  reduced  by 
Tafel 1  in  50%  sulphuric  acid.  He  obtained  desoxytheobro- 
mine,  or  3.7-dimethyl-2-oxy-1.6-dihydropurin: 

NH-CH2 

I         |    CH3 
CO     C-N\ 
I         II       >H. 
CH3N  -  V-W 

3.7-Dimethyl-2-oxypurin  is  formed  on  oxidation  with  an  excess 
of  silver  acetate. 

Caffeine,  or  1.3.7-Trimethylxanthine,  was  reduced  in  50% 
sulphuric  acid  to  desoxy caffeine  by  Tafel  and  Baillie,2  while 
they  were  investigating  the  reduction  of  acylamines  to 
alkylamines.  In  a  later  investigation3  they  showed  that 
desoxy  caffeine  is  to  be  designated  as  1.3.7-trimethyl-2-oxy- 
1.6-dihydropurin: 

CH3N-CH2 
I      |      CH3 
CO  C-Nv 
I     II        >H. 
CH3N-C-ISr 

By  oxidizing  it  with  lead  peroxide,  3.7-dimethyl-2-oxy- 
purin-1-methylhydroxide  is  obtained: 

OH 


CO  C-N 
CH3N-C- 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  32,  3194  (1899). 

2  Ibid.,  686  (1899). 

3  Ibid.,  3206  (1899). 


130         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

This  is  a  compound  which  corresponds  to  the  3-methyl-2- 
oxypurin  obtained  from  3-methyldesoxyxanthine.  Its  strongly 
basic  properties  are  conditioned  by  the  methyl  group  in  posi- 
tion (1).  It  may  be  here  mentioned  that  Tafel  has  worked 
out  his  valuable  method  chiefly  by  the  use  of  caffeine.  The 
corresponding  investigation  has  already  been  considered  (p.  24 
and  p.  52). 

Guanine,  2-amino-6-oxypurin,  when  electrolytically  reduced 
in  a  60%  -sulphuric  acid,  is  converted  into  desoxyguanine, 
a  base  containing  no  oxygen  (Tafel  and  Ach  J)  : 

NH-CO  NH-CH2 

II  II 

NH2C        C-NHV  NH2C        C-NHk 

||  •      ||  >CH  +  2H2=          ||         ||  >CH  +  H20. 

N  -  C  --  W  N  --  C  --  W 

Desoxyguanine,  2-amino-1.6-dihydropurin,  is  easily  oxi- 
dized to  2-aminopurin  : 


NH2C     C-NHX 

II      II          >H. 

N-C  -  W 

This  substance  is  isomeric  with  adenine  and  is  very  simi- 
lar to  it.  Nitrous  acid  converts  it  into  2-oxypurin,  an 
isomer  of  hypoxanthine. 

The  firm  of  C.  F.  Boehringer  &  Sohne  (Waldhof-Mannheim) 
has  patented  2  Tafel's  process  for  reducing  xanthine  bases. 

9.  DERIVATIVES  OF  CARBONIC  ACID    CONTAINING  SULPHUR. 

Potassium  Xanthate.  —  C.  Schall3  obtained,  by  the  elec- 
trolysis of  potassium  xanthate  in  aqueous  solution  and  with 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  1170  (1901). 

2  See  especially  D.  R.  P.  No.  108577  (1898)  :     Process  for  the  preparation 
of  xanthines  containing  less  oxygen  by  means  of  the  electrolytic   reduc- 
tion in  acid  solution  of  alkylated  xanthines. 

3  Zeitschr.  f.  Elektrochemie  2,  475  (1896);  3,  83  (1897). 


ELECTROLYSIS  OF  ALIPHATIC  COMPOUNDS.  131 

a  high  anode  current  density,  xanthic  supersulphide,  or  ethyl 
dioxysulphocarbonate,  as  might  be  expected: 

/OC2H5  /OC2H5C2H5(\ 

2CS<              =CS<  >CS+2K. 

\SK  XS-      $/ 

Potassium  Methyl-,  Isobutyl-,  and  Isoamylxanthate  behave 
analogously  (Schall  and  Kraszler  1).  They  are  converted  at 
the  anode  into  the  corresponding  dithiondisulphides 

RCSS— SSCR. 

These  are  non-crystallizable  oils. 

Ammonium  Dithiocarbamate  is  converted  with  difficulty 
into  thiuramdisulphide : 

(NH2CS)S-S(SCNH2); 

the  conditions  under  which  this  takes  place  have  not  yet  been 
explained. 

Diethylammonium  Diethyldithiocarbamate  is  said  to  give  at 
the  anode  tetraethylthiuramdisulphide : 

[(C2H5)  2NCS]S  -  S[SCN(C2H5)  2]. 
Potassium  Ethyltrithiocarbonate  gives  dithiondisulphide : 

(C2H5SC)S-S(CSC2H5). 

Potassium  Phenylsulphocarbazinate,  C6H5NH  •  NHCSSK, 
gives  (Schall  and  Kraszler 2)  no  disulphide,  but  diphenyl- 
thiocarbazide : 

CS(NH-NHC6H5)2. 

1  Zeitschr.  f.  Elektrochemie  5,  225  (1898).  2 1.  c. 


CHAPTER  IV. 
THE  ELECTROLYSIS  OF  AROMATIC   COMPOUNDS. 

IN  the  aliphatic  series  the  carboxylic  acids  furnish  the 
principal  material  of  electrolysis.  This  is  due  to  the  reactive- 
ness  of  their  anions,  which  readily  split  off  carbonic  acid,  thus 
affording  manifold  syntheses.  In  the  aromatic  series,  however, 
.the  nitro-compounds  are  the  more  interesting,  on  account  of 
their  easy  reducibility  and  the  importance  of  their  reduction 
products.  The  facts  which  give  to  electrochemical  reduction 
pre-eminence  over  oxidation  have  already  been  explained  in 
the  introduction  (p.  2). 

Single  oxidation  processes  have,  however,  also  become 
important.  Besides  the  oxidability  of  easily  oxidizable  sub- 
stances, for  instance  aniline,  or  easily  oxidizable  groups  like 
methyl,  the  peculiar  reaction  which  seems  to  occur  very 
frequently  in  the  electrical  oxidation  in  sulphuric  acid,  and 
which  consists  of  the  entrance  of  oxygen  into  the  benzene 
nucleus,  must  be  emphasized.  Hydrocarbons,  phenols,  quin- 
ones,  and  azo-compounds  seem  to  behave  alike  in  this  respect. 

Electrolytic  ^substitutions  furnish  a  further  general  point  of 
view. 

Although  the  substitution  processes  afforded  by  the  action 
of  the  primarily  discharged  anion  of  an  inorganic  salt  upon  an 
organic  body  are  to  be  included  among  the  simpler  reactions, 
the  results  obtained  so  far  in  this  domain  have  been  very  scanty, 
especially  in  regard  to  aromatic  substances.  The  above- 
mentioned  investigations  of  Elbs  and  Hertz,  as  well  as  those  of 
Forster  and  Mewes  on  the  electrolytic  preparation  of  iodoform, 

132 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        133 

can  serve  as  an  indication  that  many  interesting  and  remunera- 
tive problems  yet  await  solution  in  this  field. 

1.  HYDROCARBONS. 

Benzene. — Renard,1  by  the  anodical  action  of  the  current 
in  an  alcohol-sulphuric-acid  solution  of  benzene  with  platinum 
anodes,  obtained  a  body  melting  at  171°  which  Gattermann  and 
Friedrichs2  recognized  later  as  hydroquinone.  The  latter  is 
also  formed  (Kempf 3)  if  a  mixture  of  benzene  and  a  10% 
sulphuric  acid  is  electrolyzed  at  lead-peroxide  anodes  and  lead 
or  zinc  cathodes.  Quinone  is  first  produced  at  the  anode  with 
the  aid  of  the  lead  peroxide.  It  is  then  reduced  at  the  cathode 
to  hydroquinone. 

The  process  very  likely  occurs  in  the  same  way  at  a  platinum 
anode.  Hydroquinone  itself,  when  oxidized  electrolytically, 
yields  only  traces  of  quinone  (Liebermann  4),  quinhydrone 
being  the  chief  product. 

However,  it  is  not  impossible  that  at  platinum  anode8 
a  direct  introduction  of  hydroxyl  groups  into  the  benzene 
nucleus,  i.e.  a  primary  formation  of  hydroquinone,  takes 
place,  especially  if  concentrated  sulphuric  acid  is  chosen  as 
the  electrolyte.  Chemical  as  well  as  electrochemical  experi- 
ences indicate  this.  Thus,  by  means  of  per  sulphuric  acid  or 
its  salts,  obtained  by  the  electrolysis  of  sulphuric  acid  or  its 
salts,  nitrophenol  can  be  directly  converted  into  nitrohydro- 
quinone,  salicylic  acid  into  hydroquinonecarboxylic  acid, 
anthraquinone  into  alizarin,  and  this  latter  into  alizarin-bor- 
deaux and  alizarin-cyanine. 

It  may  be  here  mentioned  that  oxygen  can  thus  be  electro- 
lytically  introduced  into  azobenzene.  Heilpel-n,5  by  electrolyzing 
azobenzene  in  concentrated  sulphuric  acid,  obtained  tetraoxy- 


1  Compt.  rend.  91,  175  (1880). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  1942  (1894). 

3  D.  R.  P.  No.  117251  (1899). 
4Ztschr.  f.  Elektrochemie  2,  497  (1896). 
5  Ibid.  4,  89  (1879). 


134         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

azobenzene,  a  fast  dye,  soluble  in  concentrated  sulphuric  acid 
with  a  cherry-red  color  and  resistant  to  the  action  of  light  and 
acids. 

Toluene. — According  to  Renard,1  this  compound,  by  elec- 
trolytic oxidation  in  alcoholic-sulphuric  acid,  forms  benzaldehyde 
and  phenose,  C6H6(OH)6(?).  According  to  Puls,2  there  are  pro- 
duced in  the  same  electrolyte,  using  a  diaphragm  and  a  platinum 
anode,  benzaldehyde,  benzoic  acid,  benzoic  ethyl  ester,  and,  as 
chief  product,  p-sulphobenzoic  acid.  Under  the  same  con- 
ditions, Merzbacher  and  Smith3  had  obtained  a  poor  yield  of 
benzoic  ethyl  ester. 

Law  and  Mollwo  Perkin  4  report  on  the  electrolytic  oxidation 
of  toluene,  the  three  xylenes,  mesitylene,  and  pseudocumene. 
In  a  sulphuric-acid-acetone  solution  of  toluene  they  obtained 
a  little  benzaldehyde  and  perhaps  benzyl  alcohol.  The  elec- 
trolysis of  an  emulsion  of  toluene  and  dilute  sulphuric  acid 
leads  to  a  complete  combustion  of  the  toluene  to  carbonic  acid 
and  water. 

The  three  xylenes,  electrolyzed  in  acetone  and  dilute  sul- 
phuric acid,  yield  principally  the  three  toluic  aldehydes,  m- 
Xylene,  even  when  sodium  acetate  and  acetic  acid  are  employed 
as  electrolyte,  gives  the  m-toluic  aldehyde. 

Pseudocumene,  in  the  presence  of  acetone  and  sulphuric  acid, 
gives  apparently  a  mixture  of  the  three  isomeric  dimethyl- 
benzaldehydes.  Analogously,  mesitylene  is  oxidized  to  mesity- 
lenic  aldehyde. 

Naphthalene. — This  substance,  electrolyzed  by  Panchaud 
de  Bo t tens  5  in  a  sulphuric-acid-acetone  solution  at  platinum 
and  lead  anodes,  gives,*  besides  a  brown  by-product,  principally 
a  little  a-naphthoquinone.  In  glacial-acetic-sulphuric  acid 
traces  of  phthalic  adid  are  formed  at  platinum  electrodes. 


1  Compt.  rend.  91,  175  (1880). 

2  Chem.  Ztg.  25,  263  (1901). 

3  Journ.  Am.  Chem.  Soc.  22,  723  (1900). 

4  Trans,  of  the  Faraday  Soc.  I  (25/10,  1904). 
6  Ztschr.  f.  Elektrochemie  8,  673  (1902). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        135 


2.    NlTRO-   AND   NlTROSO-COMPOUNDS. 

Of  all  organic  substances  which  have  been  tested  as  to 
their  behavior  towards  the  action  of  the  electric  current, 
aromatic  nitro-compounds  have  received  the  most  accurate 
treatment  and  attained  the  greatest  importance.  The  reason 
for  this  lies,  on  the  one  hand,  in  the  fact  that  the  nitro-group, 
being  extremely  reducible,  reacts  only  at  the  cathode,  whereby 
the  end-products  are  closely  and  simply  related  to  the  product 
started  with;  and,  on  the  other  hand,  in  the  variety  of  the 
reduction  phases  which  the  nitro-group  can  develop,  depending 
upon  the  conditions  of  the  experiment. 

It  thus  happens  that  the  class  of  nitro-bodies  not  only  affords 
the  greatest  number  of  important  results  and  smooth  reactions, 
and  thereby  is  of  great  importance  technically  and  for  the 
manufacturing  side  of  organic  chemistry,  but  it  also  offers  the 
suitable  starting-point  for  the  treatment  of  general  and  special 
theoretical  questions.  So  far  as  these  are  of  a  general  nature, 
treating  of  the  relation  of  the  reaction  velocity  to  the  reduction 
velocity  and  referring  to  the  importance  of  the  cathode  material, 
they  have  already  been  discussed  in  the  first  chapter.  The 
theoretical  relations,  which  are  of  importance  only  for  the 
reduction  of  nitro-bodies,  will  be  briefly  considered  here.  They 
can  be  divided  into  purely  chemical  and  electrochemical  ones. 
The  former,  which  obtain  in  every  method  for  the  reduction  of 
nitro-bodies,  deserve  mention  because  they  were  first  understood 
in  closest  connection  with  the  electrical  reduction;  they  refer  to 
chemically  possible  reduction  phases  and  their  gradation.  The 
latter  encompass  the  dependence  of  the  chemical  results  upon 
the  electrical  conditions  of  experiment  and  the  special  roles  of 
the  separate  decisive  factors. 

The  importance,  thus  shown,  of  our  knowledge  of  the 
electrical  reduction  of  nitrobenzene  in  regard  to  the  practical 
and  theoretical  exploitation  of  the  electrolysis  of  organic  sub- 
stances makes  it  desirable  to  first  give  a  short  historical  survey 


136         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

of  the  development  of  the  views  and  the  importance  of  the 
separate  observations.1 

a.  General  Observations  on  the  Reduction  of  Nitro-compounds. 

Haussermann2  reduced  nitrobenzene  and  nitrotoluenes  both 
in  alkaline  and  acid  solution,  the  former  with  iron,  the  latter 
with  platinum,  electrodes.  By  reduction  in  alkaline  solution, 
he  obtained  as  principal  product  hydrazobenzene  and  hydrazo- 
toluene  respectively;  in  sulphuric-acid  solution  he  got  from 
nitrobenzene,  as  chief  products,  benzidine  sulphate  and  azoxy- 
benzene,  besides  an  easily  changeable  body  which  was  not  further 
determined.  o-Nitrotoluene  3  under  like  conditions  gave  o-tolui- 
dine  sulphate,  besides  small  quantities  of  o-toluidine;  p-nitro- 
toluene  yielded  principally  p-toluidirie. 

Elbs,  on  the  contrary,  obtained  entirely  different  results 
when  he  electrolytically  reduced  p-nitrotoluene  and  nitrobenzene 
in  acid  and  in  alkaline  solution  with  other  cathode  metals. 
There  were  formed  in  the  reduction  of  nitrobenzene  in  alkaline 
solution  at  a  lead  or  mercury  cathode  varying  quantities  of 
azoxy-  and  azobenzene,  the  former  mostly  preponderating. 
p-Nitrotoluene  behaves  similarly  if  reduced  in  the  same  manner, 
—p-azoxy-  and  p-azotoluene  being  produced.  The  reduction 
takes  place  much  more  slowly  and  less  completely  in  this  case 
than  when  nitrobenzene  is  used.  Haussermann  observed  the 
same  with  o-nitrotoluene.  "  o-Nitrophenol  behaves  quite  differ- 
ently; the  chief  product  is  o-amidophenol,  besides  red  and 
i>rown  substances  which  could  not  be  obtained  pure.  In  the 
reduction  of  nitrobenzene  in  sulphuric-acid  solution  Elbs 
employed  a  zinc  cathode  and  obtained  chiefly  aniline. 

Elbs4  draws  the  following  conclusion:  "  Without  consider- 
ing the  other  conditions  of  experiment,  the  kind  of  metal 

1  This  classification  (a)  has  been  partially  taken  from  the  dissertation 
of  my  pupil  Jos.  Schmitt:  "Concerning  the  Importance  of  the  Cathode 
Material  in  the  Electrolytic  Reduction  of  m-  and  p-Nitrotoluene,"  Bonn,  1904. 

2Chem.  Ztg.  17,  129,  206  (1893). 

3  Ibid.,  209  (1893). 

n.  c. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        137 

employed  as  electrode  seems  to  exert  an  important  influence, 
since  Haussermann  obtained  benzidine  and  azoxybenzene 
from  nitrobenzene  at  a  platinum  electrode."  Gattermann 
and  Koppert,1  by  electrolytically  reducing  nitrobenzene  in  con- 
centrated sulphuric  acid  with  the  addition  of  a  few  drops 
of  water,  obtained  other  results.  After  several  hours'  electrol- 
ysis the  contents  of  the  earthenware  cell,  which  contained 
the  reduction  fluid  together  with  a  platinum  cathode,  solidi- 
fies, forming  a  colorless  mass  of  crystals  of  p-amidophenoL 
sulphate,  which  was  permeated  by  a  blue-green  liquid. 

After  these  observations,  Gattermann  and  his  pupils 2; 
continued  their  investigation  on  the  reduction  of  aromatic 
nitro-bodies  to  amidophenol  derivatives.  They  thus  examined 
mono-  and  dinitrohydrocarbons,  nitroamines,  nitrocarboxylic 
and  nitrosulphonic  acids,  also  the  esters  of  the  acids.  After 
the  reaction  had  been  successfully  tested  in  over  40  cases  it 
was  adjudged  to  be  of  general  applicability. 

The  important  result  of  these  experiments  is  that  nearly 
all  nitro-bodies  with  an  unoccupied  para-position  are  con- 
verted by  electrolytic  reduction  in  concentrated  sulphuric 
acid  into  p-amidophenol  derivatives,  i.e.  not  only  is  the  nitro- 
group  reduced  completely  to  the  amido-group,  but  in  most 
cases  the  hydrogen  atom  in  p-position  to  the  amido-group  is 
simultaneously  substituted  by  the  hydroxyl  group. 

A  short  time  after  the  publication  of  the  interesting  experi- 
ments of  Gattermann,  A.  A.  Noyes  and  A.  A.  Clement  3  made 
known  their  studies  on  the  electrolytic  reduction  of  nitro- 
benzene in  sulphuric-acid  solution. 

Noyes  and  Clement  used  concentrated  sulphuric  acid  of 
1.84  to  1.94  sp.  gr.  as  a  solvent  for  nitrobenzene.  Gatter- 
mann and  Koppert  had  treated  the  sulphuric-acid  solution 
before  the  reduction  with  a  few  drops  of  water.  Noyes  and 
Clement  obtained  from  50  g.  nitrobenzene  at  platinum  elec- 
trodes 30  g.  anhydrous  p-amidophenol-o-sulphonic  acid,  Cor- 

1  Chem.  Ztg.  17,  210  (1893). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  26, 1844,  2810  (1893);  27, 1927  (1894). 

3  Ibid  26,  990  (1893). 


138         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

responding  to  a  yield  of  40  per  cent,  of  the  theoretically  pos- 
sible quantity. 

Three  years  later  Elbs1  reverted  to  the  experiments  of 
Gattermann.  On  repeating  the  same  he  obtained,  indeed, 
the  same  results,  but  simultaneously  observed  that  consider- 
able quantities  of  aniline  are  always  formed  besides  the  p-ami- 
dophenol.  When  Elbs  used  glacial  acetic  acid  as  a  diluent  of 
the  sulphuric  acid  he  found  a  considerable  increase  in  the 
yield  of  p-amidophenol,  but  the  yield  of  aniline  kept  apace 
of  that  of  the  latter.  If  he  used  a  lead  in  place  of  a  platinum 
cathode,  the  reduction  was  accelerated,  being  favorable  to 
the  aniline  formation  at  the  expense  of  the  p-amidophenol. 

Lob2  found  a  reaction  analogous  to  that  of  Gattermann 
when  he  reduced  nitrobenzene  in  hydrochloric-acid  solution 
or  suspension,  using  platinum  electrodes. 

In  this  process  there  is  formed  as  chief  product  a  mixture 
of  o-  and  p-chlor  aniline.  The  formation  of  this  can  be  explained 
thus:  The  primarily  formed  phenylhydroxylamine  reacts  with 
the  hydrochloric  acid,  simultaneously  rearranging  itself: 

C6H5NHOH  +  HC1  =  C6H5NHC1  +  H20. 
C6H5NHC1-*C1C6H4NH2. 

The  same  mechanism  of  molecular  rearrangement  must 
be  assumed  in  Gattermanns  reaction: 


Direct  proof  of  the  correctness  of  this  view  was  produced 
by  Gattermann3  on  adding  benzaldehyde  to  the  solution  of 
nitrobenzene  in  sulphuric  acid.  Benzylidenephenylhydroxyl- 
amine  is  formed: 


C6H5NHOH  +  OHCC6H5  =  C6H5  -  N—  HC  -  C6H5  ; 

1  Ztschr.  f.  Elektrochemie  2,  472  (1896). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  1894  (1896). 

3  Ibid.,  3034,  3037,  3040   (1896). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        139 

i.e.  the  condensation  product  of  phenylhydroxylamine  with 
benzaldehyde. 

A  similar  influence  of  the  cathode  material,  as  observed 
by  Elbs  in  replacing  the  platinum  electrode  by  a  lead  cathode 
in  sulphuric-acid  solution,  was  found  by  Lob  1  when  he  used 
a  lead  cathode  in  hydrochloric-acid  solution.  No  chloraniline 
was  formed,  aniline  being  produced  almost  exclusively. 

Further  observations  concerning  the  influence  of  the  cathode 
material  in  reductions  were  made  by  Lob 2  in  his  studies  on 
the  electrolytic  preparation  of  benzidine.  His  results  are 
briefly  the  following: 

1.  Platinum    and    nickel    electrodes    behave    alike    in    the 
experiments  to  reduce  nitrobenzene  in  acid  solution  to  ben- 
zidine.    Carbon   cathodes,    on   the   contrary,   give   only  little 
benzidine;    zinc   and  amalgamated  zinc  electrodes  yield  no, 
or  extremely  little,  benzidine,  while  aniline,  as  already  pre- 
viously observed  by  Elbs,  results  as  the  principal  product. 

2.  Mercury,  nickel,  copper,  zinc,  lead,  iron,  brass,  and  zinc 
amalgam  were  tried  as  electrode  material  in  respect  to   their 
reduction  behavior  in  the  reduction  of  azobenzene  to  benzi- 
dine in  alcohol-sulphuric — acid    solution.     It  was  shown  that 
the  furthest  utilizable  reduction  was  obtained  with  mercury; 
the  usefulness  of  the  other  metals  was  determined  to  be  in 
the  following  order:    Lead,   sheet    nickel,   nickel-wire    gauze, 
copper,  zinc,  iron,  and  brass. 

3.  In  the  reduction  experiments  of  nitrobenzene  to  azo- 
benzene in  alkaline-alcoholic  solution  mercury  electrodes  prove 
good;   however,    nickel-wire — gauze   electrodes   give   excellent 
results.     This  had  been  already  shown  by  Elbs.3 

4.  The  same  is  true  in  the  reduction  of  nitrobenzene  to 
azoxy benzene  in  an  alkaline  aqueous  suspension. 

Finally,  the  employment  of  a  strong  hydrochloric  acid  and 
a  tin  cathode,  or  an  unattackable  cathode  with  addition  of 


1  Ztschr.  f.  Elektrochemie  4,  430  (1898). 

2  Ibid.  7,  337,  597  (1900-1901). 

3  Ibid.  5,  108  (1898). 


140         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

stannous  chloride,  was  ascertained  to  constitute  a  favorable 
condition  for  the  reduction  of  azoxybenzene  and  azobenzene 
to  benzidine. 

The  practical  results  of  all  these  investigations  for  the 
reduction  of  nitrobenzene  and  its  reduction  phases  are  briefly 
the  following: 

At  attackable  electrodes,  like  zinc,  lead,  and  tin,  the  reduc- 
tion generally  proceeds  further  than  at  unattackable  electrodes, 
such  as  platinum,  nickel,  and  mercury.  The  attempts  to 
utilize  technically  these  properties  of  the  cathode  metals  for 
a  series  of  nitro-bodies  led  to  important  patents. 

Thus  Boehringer  &  Sohne  1  (Mannheim)  patented  a  process 
by  which,  when  employing  tin-cathodes  (or  cathodes  of  other 
indifferent  metals  with  an  addition  of  a  small  quantity  of  a 
tin  salt),  fatty  or  aromatic  nitro-compounds,  dissolved  or 
suspended  in  aqueous  or  hydro-alcoholic  hydrochloric  acid, 
can  be  reduced  in  almost  theoretical  yields  to  the  correspond? 
ing  amines. 

In  hydrochloric-acid  solution,  as  already  mentioned,  chlor. 
anilines  are  produced  at  platinum  electrodes. 

According  to  another  patent2  of  the  same  firm,  copper, 
lead,  iron,  chromium,  and  mercury  can  be  used  instead  of  tin, 
if  these  metals  are  added  in  the  form  of  their  salts  or  as  a  finely 
divided  powder  to  the  cathode  electrolyte. 

After  the  publication  of  these  patents  Elbs  and  Silbermann  3 
reported  that  if  a  lead  cathode  in  sulphuric  acid  is  employed, 
the  same  results  are  attained.  It  proved  to  be  true  that  in 
order  to  obtain  the  best  yields  of  aniline  diluted  alcohol  served 
as  a  better  diluent  for  the  sulphuric  acid  than  the  glacial  acetic 
acid  formerly  employed.  Zinc  behaves  in  sulphuric-acid  solu- 
tions like  lead;  however,  the  precipitation  of  difficultly  solu- 
ble zinc  double  salts  is  a  hindrance.  Elbs  likewise  obtained 
90  per  cent  of  the  theoretical  yield  of  toluidines  from  o-  and 


*D.  R.  P.  No.  116942  (1899). 
2D.  R.  P.  No.  117007  (1900). 
3  Ztschr.  f.  Elektrochemie  7,  589  (1901). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        141 

m-nitrotoluene ;  the  yield  from  p-nitrotoluene  was  a  few  per 
cent.  less. 

A  supplementary  patent  of  Boehringer  &  Sohne  1  extends 
the  process  of  the  D.  R.  P.  No.  116942  to  the  reduction  of 
azo-bodies  to  amines. 

The  patent  claim  is  as  follows:  "  Process  for  the  reduction 
of  azo-bodies  to  the  corresponding  amines;  consisting  in 
reducing  azo-bodies  in  acid  solution  by  simultaneously  con- 
ducting a  constant  electric  current  either  with  a  tin  cathode, 
or  with  an  indifferent  cathode  and  the  addition  of  a  tin  salt 
or  pulverized  metallic  tin." 

In  a  'later  patent 2  C.  F.  Boehringer  &  Sohne  point  out  that 
the  nitro-compounds  in  acid  solution  can  not  only  be  reduced  to 
amines  with  such  metals  as  easily  evolve  hydrogen  with  dilute 
acids,  but  also  with  copper.  This  fact  offers  particular  technical 
advantages,  because  copper  can  be  most  easily  and  completely 
regenerated  electrolytica  ly  from  the  liquors.  While  in  the 
above-mentioned  methods  the  reduction  to  the  amines  is  made 
in  acid  solution,  C.  F.  Boehringer  &  Sohne  have  obtained  a 
patent  3  according  to  which  it  is  also  possible  to  reduce  nitro- 
bodies  to  the  corresponding  amines  -in  alkaline  and  alkali-salt 
suspension,  if  a  copper  cathode  with  or  without  the  addition 
of  copper  powder  is  employed. 

According  to  an  investigation  by  Elbs  and  Brand,4  the 
addition  of  copper  powder  is  absolutely  necessary  for  obtaining 
the  desired  effect. 

In  1899  the  Farbenfabriken  vorm.  Friedr  Bayer  &  Co.5 
(Elberfeld)  patented  a  process  for  electrolytically  preparing  azo- 
and  hydrazo-compounds  The  method  is  characterized  by  the 
fact  that  the  nitro-body  to  be  reduced  is  held  suspended  in  the 
alkaline  cathode  liquid,  and  is  reduced  during  continuous  vigor- 


1  D.  R.  P.  No.  121835  (1900).     See    also    the    English    Pat.    No.    19879 
(1901). 

2  D.  R.  P.  No.  127815  (1901). 
3D.  R.  P.  No.  130742  (1901). 

*  Ztschr.  f.  Elektrochemie  8,  789  (1902). 
BD.  R.  P.  No.  121899  (1899). 


142         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

ous  stirring  and  the  addition  of  a  metallic  oxide  solution  of  zinc, 
tin,  or  lead. 

This  method  was  then  extended  by  a  supplementary  patent,1 
according  to  which  the  reduction  of  aromatic  nitro-bodies  is 
carried  out  in  aqueous  alkaline  suspension  instead  of  in  the 
presence  of  alkali-soluble  oxides  of  the  heavy  metals  and  the 
use  of  such  metal  cathodes  the  oxides  of  which  are  soluble  in 
alkalies. 

It  is  very  evident,  from  all  these  observations,  what  influence 
the  cathode  material  exercises  on  the  obtainable  reduction 
phase  of  nitrobenzene  and  its  derivatives.  There  is  no  lack  of 
attempts  to  explain  this  influence.  The  expressed  opinions  can 
be  grouped  under  three  points  of  view: 

1.  The  specific  action  of  the   cathode  metal  is  a  purely 
chemical  function. 

2.  It  is  a  purely  electric  function,  and  depends  upon  the 
potential  values  obtainable  on  the  various  metals. 

3.  A  summation  of  electrical  and  chemical  influences  occurs. 

Elbs  2  defends  the  first  view.  He  explains  the  aniline  forma- 
tion at  lead  and  zinc  cathodes  in  sulphuric-acid  solution  in  the 
following  manner : 

' '  We  will  have  to  suppose  that  the  lead  sponge  occurring  at 
the  lead  cathode  reduces  the  nitrobenzene  to  aniline.  Men- 
tionable  quantities  of  lead  sulphate  cannot  be  found,  since  this 
is  continually  reconverted  to  lead  sponge  by  the  freed  hydrogen 
ions.  This  process  is  analogous  to  the  one  previously  published 
by  me 3  in  which  a  hydro-alcoholic  solution  of  nitrobenzene 
acidified  with  sulphuric  acid  gives  aniline  when  a  zinc  cathode 
is  used.  Considerable  quantities  of  zinc  sulphate  do  not  occur. 
At  a  platinum  cathode,  under  the  same  conditions,  no  aniline  is 
formed,  but  azoxybenzene  and  hydrazobenzene  or  benzidine 
form.  This  has  been  confirmed  by  Haussermann."  4 

The  explanation  attempted  by  Elbs  agrees  in  general  with 

1  D.  R.  P.  No.  121900  (1899). 

2  Ztschr.  f.  Elektrochemie  2,  474  (1896). 

3  Chem.  Ztg.  17,  209  (1893). 

4  Ibid.,  129  (1893). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        143 

that  advanced  in  the  specifications  of  C.  F.  Boehringer  &  Sohne's 
patents,  D.  R.  P.  No.  116942  and  No.  117007: 

"If  attackable  cathodes  of  metallic  tin  are  employed,  tin  is 
dissolved  continually  at  the  cathode  during  the  simultaneous 
reduction  of  the  nitro-body  so  long  as  unchanged  nitro-com- 
pounds  are  present.  The  metal  is,  however,  immediately 
precipitated  again  on  the  cathode  in  the  form  of  spangles  or  mud. 
When  an  unattackable  cathode,  say  nickel,  is  used,  and  stannous 
chloride  added,  metallic  tin  is  first  precipitated  on  the  cathode; 
the  process  following  then  resembles  the  one  above  explained. 
A  transition  of  positively  laden  tin  ions  from  the  cathode  into  the 
electrolyte  follows,  and  a  deposition  of  tin  ions  at  the  same 
place.  Very  small  quantities  of  tin  hence  suffice  for  reducing 
any  desirable  quantity  of  a  nitro-body. " 

Haber,1  on  the  basis  of  extensive  experiments,  defends  the 
opinion  that  only  the  cathode  potential  is  decisive  for  the 
obtainable  reduction  phase.  This  investigator,  by  carrying  out 
the  reduction  of  nitrobenzene  in  acid  and  in  alkaline  solutions 
with  variable  and — in  several  experiments — constant  cathode 
potentials,  succeeded  in  proving  that,  depending  upon  the 
chosen  cathode  potential,  the  reduction  can  be  directed  at  will 
to  the  several  reduction  stages.  He  was  thus  able  to  determine 
the  dependence  of  the  formation  of  phenylhydroxylamine, 
azoxybenzerie,  hydrazobenzene,  and  aniline  upon  the  cathode 
potential,  and  thus  obtained  an  insight  into  the  reduction  stages 
in  the  case  of  nitrobenzene.  Aided  by  the  researches  of  Bam- 
berger,  he  was  thus  led  to  a  clear  understanding  of  the  grada- 
tion occurring  in  the  reduction  of  nitrobenzene. 

Lob,2  by  reason  of  his  experiments  with  Moore,  coincides 
with  Haber 's  opinion,  but  he  proceeds  from  other  considerations 
concerning  the  reduction  mechanism  (see  p.  14). 

The  third  opinion  was  advanced  by  Chilesotti3  and  Tafel.4 

1  Ztschr.  f.  Elektrochemie  4,  506  (1898);  Ztschr.  f.  phys.  Chemie  32,  193, 
271  (1900). 

2. Ztschr.  f.  phys.  Chemie  47,  418  (1904). 

3  Ztschr.  f.  Elektrochemie  7,  768  (1901). 

4  Ztschr.  f.  anorg.  Chemie  21,  289  (1902). 


144         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

According  to  this  view,  electrical  and  chemical  influences  can 
be  simultaneously  active. 

Chilesotti,  in  order  to  determine  the  purely  chemical  action 
of  the  metals,  subjected  nitrobenzene  and  also  phenylhydroxyl- 
amine,  formed  intermediately  in  the  electrolytic  reduction,  to 
the  action  of  electrolytically  prepared  copper  sponge  in  alcoholic 
hydrochloric-  or  sulphuric-acid  solution.  The  copper  sponge  was 
that  formed  at  the  cathode  when  a  copper  electrode  is  employed, 
or  when  a  copper  salt  is  added  to  the  electrolyte.  He  found 
that,  chemically,  copper  can  reduce  nitrobenzene  only  with  a  very 
insignificant  velocity;  phenylhydroxylamine,  on  the  contrary, 
was  almost  completely  reduced  to  aniline  in  a  very  short  time. 
He  concludes :  "  Judging  from  these  experiments,  the  progress  of 
the  reactions  in  the  process  for  electrolytically  reducing  aromatic 
nitro-compounds  to  amines,  primarily  in  the  presence  of  copper 
or  ferric  salts,  can  be  summed  up  in  the  following  manner: 
The  current  at  first  reduces  the  nitro-body  to  phenylhy- 
droxylamine (which  also  happens  in  the  absence  of  the  mentioned 
salts)  and  simultaneously  deposits  spongy  copper  or  produces 
ferrous  salt.  These  in  turn  now  reduce,  in  a  purely  chemical 
way  and  during  electrolysis  (as  shown  by  the  experiments), 
the  phenylhydroxylamine  very  rapidly  to  the  amine.  Hereby 
they  again  revert  to  the  copper  or  ferric  ion  and  are  again  subject 
to  the  current  action.  It  remains  an  open  question,  and  one 
that  cannot  at  least  be  directly  negatived,  whether  the  current 
action  can  also  at  the  same  time  and  primarily  effect  the  reduc- 
tion of  phenylhydroxylamine  to  the  amine  at  the  cathode 
potential  given  by  the  copper  or  ferrous  salt.  Thus  we  can  also 
suppose  in  the  case  of  tin,  lead,  or  zinc  electrodes,  that  in  their 
presence  or  in  that  of  their  salts  the  current  can  primarily  form 
phenylhydroxylamine.  The  deposited  metals  can  now  reduce 
chemically  both  this  compound  and  the  nitro-compound.  They 
would  very  likely  prefer  the  former,  since  they  could  apparently 
carry  out  this  reduction  with  the  greatest  velocity." 

Tafel,  by  reason  of  his  experiments  on  the  reduction  of  nitric 
acid  in  the  presence  of  sulphuric  acid,  is  inclined  to  this  view. 
He  found  that  nitric  acid  in  sulphuric-acid  solution  and  at  a 


THE  ELECTROLYSIS   OF  AROMATIC  COMPOUNDS.        145 

lead  cathode  is  primarily  reduced  almost  exclusively  to  hy- 
droxylamine,  which  can  only  with  great  difficulty  be  changed 
electrolytically  into  ammonia.  At  copper  electrodes  ammonia 
exclusively  is  formed.  Since  nitric  acid  cannot  be  reduced  to 
hydroxylamine  to  any  appreciable  extent  chemically  by  copper, 
nor  electrically  at  copper  electrodes,  Tafel  supposes  that  an 
intermediate  product  is  formed  in  the  electrolysis  of  nitric  acid; 
possibly  dihydroxylamine  NH(OH)2  possesses  the  property  of 
being  chemically  reduced  by  copper  to  ammonia.  Thus  the 
reduction  to  hydroxylamine  would  be  a  purely  electrical  process, 
while  the  formation  of  ammonia  at  copper  electrodes  depends 
on  a  combination  of  electrical  and  chemical  reductions. 

Two  important  results  can  be  derived  from  all  these  investi- 
gations :  The  certain  insight  into  the  course  of  the  reduction  of 
the  single  phases  and  the  clear  knowledge  of  the  importance  of 
the  cathode  potential. 

Since  the  decisive  relations  have  been  worked  out  with 
the  simplest  representative  of  a  nitro-body,  nitrobenzene,  the 
necessary  data  on  this  substance  will  be  discussed  first,  and 
these  data  will  be  supplemented  so  far  as  necessary  under  the 
derivatives  of  nitrobenzene. 

b.  The  Reduction  of  Nitrobenzene. 
I.  Chemical  Relations. 

The  course  of  electrical  reduction,  like  that  of  purely  chem- 
ical reduction,  depends  decisively  upon  whether  the  reduction  is 
carried  out  in  an  alkaline  or  acid  solution.  But  these  relations 
are  of  a  positive  nature  in  electrolysis  only  so  long  as  they  are 
not  compensated  by  the  electrical  factors,  such  as  cathode 
material  and  potential.  To  avoid  a  complication,  it  is  necessary 
to  limit  the  considerations  primarily  to  unattackable  cathodes 
and  to  take  no  account  of  an  adjustment  to  certain  and  constant 
cathode  potentials,  and  to  exclude  a  secondary  interference  of 
the  solvent,  for  instance  by  molecular  rearrangements.  In 
this  general  comprehension  of  the  problem  it  can  be  said 
that  the  well-known  chemical  rule  reoccurs  in  electrolytical 


146         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

reduction;  viz.,  in  acid  solution  the  formation  of  aniline  is 
favored,  in  alkaline  solution  that  of  azoxy-  and  azobenzene. 

Lob  l  has  tried  to  explain  these  facts  on  the  basis  of  the 
electrolytic  dissociation  theory.  He  emphasizes  the  fact  that 
in  alkaline  solution  sodium  ions,  in  acid  solution  hydrogen 
ions,  tend  chiefly  to  effect  reduction.  In  the  latter  case  the 
possibility  of  hydrogen  addition,  which  facilitates  the  forma- 
tion of  hydrazo-  and  amido-compounds,  is  present  on  a  large 
scale.  Even  if  these  considerations,  particularly  the  suppo- 
sition that  in  alkaline  electrolytes  the  sodium  ions  form  pri- 
marily the  reducing  agent,  are  thoroughly  established,  they 
seem  unsuitable  as  a  basis  of  a  general  theory  of  reduction, 
because  Haber  has  proved  by  thorough  investigations  that 
the  typically  alkaline  reduction  products,  azoxy-  and  azo- 
benzene, possess  a  secondary  character, — do  not  belong  to 
the  normal  course  of  reaction,  but  are  first  formed  by  the  con- 
densations of  normal  reduction  phases.  Since  Haber  has 
also  shown  that  the  primary  reduction  products  in  alkaline 
and  acid  electrolytes  are  the  same,  the  divergencies  in  the 
results  can  be  explained  only  by  the  unequal  reaction  veloci- 
ties with  which  the  mentioned  condensations  occur,  so  that 
in  this  the  influence  of  the  sodium  ions  and  hydrogen  ions 
shows  itself. 

We  are  indebted  to  the  labors  of  Bamberger  and  his  pupils  2 
and  to  Haber's  3  extensive  investigations  for  the  explanation 
of  the  reduction  mechanism. '- 

The  typical  order  in  alkaline  and  in  acid  reduction  is: 
Nitrobenzene— >nitrosobenzene— >phenylhydroxylamine  — »aniline. 
However,  further  reductions  which  often  interrupt  the  smooth 
progress  of  the  process  from  nitrobenzene  to  aniline  occur  be- 
tween these  simple  reduction  products.  A  number  of  possi- 
bilities hinder  the  appearance  of  the  above-mentioned  typical 
reaction  scheme  unless  especial  conditions  are  created;  thus 

1  Ztschr.  fur  Elektrochemie  3,  39  (1 896) . 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  31,  1500,  1522  (1898);  33,  274  (1900) 
et  al. 

3  Ztschr.  f.  Elektrochemie  4,  511  (1898);  Ztschr.  f.  phys.  Chem.  32,  271 
(1900). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        147 

in  the  first  instance  the  condensation  of  nitrosobenzene  with 
phenylhydroxylamine  to  azoxybenzene,  which  is  further  re- 
ducible to  hydrazobenzene;  also  the  reaction  of  the  hydrazo- 
benzene  thus  produced  with  unchanged  nitro-  or  nitrosobenzene 
to  azobenzene,  which  is  likewise  a  primary  source  of  hydrazo- 
benzene; then  the  rearrangement  of  the  latter  to  benzidine, 
that  of  phenylhydroxylamine  to  amidophenol  or  its  derivatives, 
and  finally  the  capability  of  phenylhydroxylamine  to  yield 
azobenzene  in  alcoholic-alkaline  solution  with  the  splitting  off 
of  water 

The  different  processes  occur  in  varying  proportions  quan- 
titatively or  qualitatively,  depending  upon  the  nature  of  the 
electrolyte  and  of  the  cathode  material,  and  upon  the  current 
conditions. 

The  following  reduction  and  reaction  scheme  can  be  given 
in  support  of  Haber;s  descriptions  for  the  electrolytic  processes; 


C6H5NO 


C6H5NO 


C6H5NHOH- 


C6H5N  — NC6H5 

•V 


C6H5N=NC6H5. 


C6H5NH-HNC6H, 


Azoxybenzene  is  therefore  formed  by  condensation  of  nitro- 
sobenzene and  phenylhydroxylamine.  This  reaction,  like  the 
production  of  azobenzene,  takes  place  very  rapidly  under 
the  influence  of  sodium  ions;  the  ready  occurrence  of  both  of 
these  substances  in  alkaline  solution  is  thus  easily  explained. 
Azobenzene  is  mostly  produced  by  a  condensation  of  nitro- 


148         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

benzene    or   nitrosobenzene    with    hydrazobenzene,    which  in 
turn  is  a  direct  reduction  product  of  azoxybenzene  : 


-NC6H5 
NO/1 
+3C6H5N=NC6H5+3H20. 


II.  2C6H5NO+C6H5NH-NHC6H5^C6H5N-  NC6H5 

\0/ 
NC6H5+H20. 


A  splitting  off  of  water,  especially  in  alcoholic-alkaline 
solution,  readily  converts  phenylhydroxylamine  into  azo- 
benzene  : 

2C6H5NHOH  -2H20-^C6H5N  =NC6H5. 

Azobenzene,  like  azoxybenzene,  can  also  pass  into  hydrazo- 
benzene, and  further  to  aniline.  In  acid  solution  the  mo- 
lecular rearrangements  readily  occur:  Phenylhydroxylamine  to 
amidophenol,  and  hydrazobenzene  to  benzidine  and  diphen- 
yline.  If  the  problem  is  to  obtain  certain  reduction  phases,  the 
task  will  be  to  determine  those  conditions  of  experiment  which 
will  reduce  as  far  as  possible  the  velocity  of  all  competing 
reactions.  Thus,  if  we  designate  all  processes  which  deviate 
from  the  straight  reduction  path  —  nitrobenzene  ^^nitroso- 
benzene— ^phenylhydroxylamine—  ^aniline  —  as  secondary  conden- 
sations and  secondary  rearrangements,  the  following  conditions 
will,  for  example,  be  presented  as  suitable  for  the  preparation 
of  aniline:  Very  high  reduction  velocity,  combined  with  very 
low  condensation  velocity  (avoidance  of  azoxybenzene  and 
azobenzene)  and  very  trifling  rearrangement  velocity  (avoid- 
ance of  amidophenol). 

In  like  manner  the  conditions  are  to  be  varied  according 
to  the  object  in  view:  to  obtain  azoxybenzene  the  reduction 
velocity  must  be  lowered,  and  the  condensation  velocity 
increased.  The  means  by  which  we  can  accomplish  at  will 
this  or  that  reaction  will  more  accurately  be  explained  under 
the  individual  reduction  phases. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        149 

II.  Significance  of  the  Electrical  Relations. 

It  is  evident  that  the  whole  connection  between  experi- 
mental conditions  and  the  obtainable  reduction  phase  is  regu- 
lated by  the  reaction  velocities  of  the  competing  processes. 
The  possibility  of  the  formation  of  each  reduction  product 
is  always  present  in  the  reduction  of  nitrobenzene;  only 
those  products,  however,  can  become  the  principal  products 
which  are  so  rapidly  produced  that  the  other  possible  processes 
cannot  find  time  to  take  place  to  any  appreciable  extent. 
Thus  only  aniline  will  be  principally  produced  if  the  inter- 
mediately occurring  phenylhydroxylamine  is  not  rearranged 
more  quickly  than  the  reduction  takes  place.  Inversely, 
to  obtain  amidophenol,  the  rearrangement  velocity  must  be 
so  increased  that  the  reduction  velocity  of  phenylhydroxyl- 
amine will  be  trifling. 

The  point  is  to  determine  the  factors  upon  which  the 
velocity  of  reaction  leading  to  the  separate  phases  depends. 

This  question  can  be  divided  and  simplified.  It  is,  therefore, 
apparent  that  a  whole  series  of  circumstances  must  be  decisive. 
The  nature  of  the  cathode  will  regulate  the  actual  reduction 
speed  (p.  11  et  seq.),  either  by  furnishing  the  reducing  ions,  or  by 
influencing  catalytically  the  reaction  between  the  discharged 
ions  and  the  depolarizer,  or  by  both  influences  making  them- 
selves felt  simultaneously.  The  concentration  of  the  acid 
influences  the  velocity  of  rearrangement,  either  of  that  of 
the  phenylhydroxylamine  or  of  the  hydrazobenzene.  The 
nature  and  concentration  of  the  alkali,  and  the  presence  or 
absence  of  alcohol,  determines  the  velocity  of  the  condensa- 
tions or  of  the  splitting  off  of  water  from  phenylhydroxyl- 
amine, and  these  relations  mutually  permeate  one  another.  If 
the  problem  can  thus  be  subdivided  into  individual  problems, 
it  can  also  be  considerably  simplified  by  the  form  of  the 
interrogation:  Is  there  one  factor  in  which  all  these  relations 
are  decisively  expressed;  is  there  one  quantity  which  determines 
clearly  the  velocities  of  the  possible  reactions  ? 

The  answer,   under   certain  limitations,   is  an  affirmative 


150         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS 

one.  The  value  of  the  cathode  potential  wholly  includes  all 
single  factors — a  certain  value  of  the  cathode  potential  corre- 
sponds to  a  wholly  certain  reduction  product,  no  matter  if  it 
occurs  primarily  or  secondarily.  To  emphasize  only  the  one 
important  point — so  long  as  a  body  acts  as  a  depolarizer  it 
acts  codeterminatively  on  the  value  of  the  potential.  If 
its  depolarizing  property  is  destroyed  by  rearrangements, 
or  by  condensations  which  have  nothing  to  do  directly  with 
the  electrical  process,  this  reaction  must  express  itself  in  the 
value  of  the  potential.  Of  course  a  certain  phase  cannot 
be  produced  under  all  conditions,  for  instance,  at  optional 
concentrations  of  the  electrolyte;  this  shows  itself  in  the 
fact  that  it  is  not  then  possible  to  obtain  the  potential  con- 
ditioning this  phase — the  potential  always  remains  the  meas- 
ure for  the  possible  effect.  However,  these  considerations 
are  only  true  provisionally  in  the  case  where  the  relation  in 
which  the  potential  stands  to  the  current  strength  and  to 
the  concentration  of  the  depolarizer  is  a  permanent  one,  which 
can  easily  be  fulfilled  by  a  suitable  choice  of  conditions.  Excep- 
tions to  the  rule  and  the  cause  of  the  exceptions  will  be  explained 
presently. 

Use  is  not  always  made  of  this  important  fact  in  practice; 
the  existing  chemical  experiences,  the  simplicity  of  the  experi- 
ments often  render  it  feasible  to  produce  the  desired  effect 
with  certainty  by  observing-.a  series  of  easily  controlled  con- 
ditions such  as  concentration,  temperature,  electrode  mate- 
rial, and  current  density — but  these  conditions  then  have 
only  the  effect  of  limiting  the  potential  to  the  values  necessary 
for  obtaining  the  result.  The  determination  of  this  relation 
required  some  time,  and  even  to-day  the  connection  between 
potential  and  reaction  velocity  is  not  recognized  by  all  inves- 
tigators.1 


1  Thus  Elbs  has  recently  referred  the  different  behavior  of  the  o-,  m-, 
and  p-compounds,  in  the  reduction  of  the  nitrotoluquinolines,  to  "  stereo- 
chemical  hindrance,"  laying  particular  weight  on  the  explanation  that  the 
course  ot  the  reduction  depends  upon  the  cathode  potential  (Ztschr.  f. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        151 

Haber  1  deserves  the  credit  of  having  determined  the 
importance  of  the  potential  at  unattackable  cathodes  in  the 
reduction  of  nitrobenzene.  Later  Lob  and  Moore2  experi- 
mentally proved  for  a  whole  series  of  cathode  metals  and 
additions  that  with  equal  cathode  potentials  the  results  are 
always  qualitatively  and  quantitatively  the  same;  but  if 
the  potential  is  neglected  the  most  varied  products  result. 
But  the  potential  is  only  a  measure  for  the  reduction  energy 
if  the  total  current  work  is  essentially  employed  for  the  reduc- 
tion process,  and  if  greater  quantities  of  it  are  not  used  up  for 
accomplishing  certain  other  work  at  the  electrodes.  Cases 
in  which  this  occurs  have  been  observed  by  Russ,3  and  by 
Haber  and  Russ.4  They  tried  to  explain  these,  as  touched 
upon  in  the  first  chapter.  It  appears,  namely,  that  the  elec- 
tric energy  necessary  for  a  certain  fixation  of  the  potential 
of  the  cathode  often  depends  not  only  upon  the  chemical 
material  of  the  cathode,  but  also  upon  its  surface  and  its  pre- 
vious treatment.  Retarding  or  accelerating  influences  can  occur 
at  the  electrode ;  a  pre-polarization  especially  can  convert  it  into 
an  active  labile  condition,  whose  cause — perhaps  the  formation 
of  a  gas  film  absorbed  by  the  electrode — has  not  yet  been 
explained.  If  the  renewal  of  such  a  gas  film,  or  more  gen- 
erally speaking,  the  restoration  of  the  changeable  electrode 
conditions,  demands  appreciable  quantities  of  the  total  work, 
the  potential  can  no  longer  serve  solely  as  an  expression  for 
the  chemical  changes  at  the  cathode. 

Lob  and  Moore  have  experimentally  proven  the  decisive 
importance  of  the  potential  in  the  reduction  of  nitrobenzene; 
the  electrodes  investigated  by  them  were  not  seriously  affected 


Elektrochemie  10,   579   (1904).      In  reality   it  is  a  question    of    competi- 
tive reaction  velocities  which  must  find  their  expression  in  the  potential. 

1  Ztschr.  f.  Elektrochemie  4,  511  (1898);  Ztschr.  f.  phys.  Chemie  32,  193 
(1900). 

2  Ztschr.  f.  phys.  Chemie  47,  418  (1904). 

3  Ibid.  44,  G41  (1903). 

4  Ibid.  47,  257  (1904). 


152         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

by  the  last-mentioned  influences.  The  results  of  their  investi- 
gation are  the  following: 

In  the  reduction  of  nitrobenzene  in  a  2%  aqueous  sodium- 
hydroxide  solution,  according  to  previous  publications,  azoxy- 
benzene  is  formed  at  platinum  and  nickel  electrodes,  azobenzene 
at  lead,  tin,  and  zinc  cathodes,  and  aniline  at  copper  cathodes, 
especially  in  the  presence  of  copper  powder. ,  It  was  found 
that,  in  an  unchangeable  experimental  arrangement,  a  cathode 
potential  of  1.8  volts,  as  ,  measured  in  connection  with  the  deci- 
normal  electrode,  could  be  carried  out  with  all  the  chosen 
cathodes  and  additions.  At  this  constant  potential,  by  using 
different  metals  and  adding  various  metallic  hydroxides,  the 
whole  reduction  was  carried  out  and  the  nature  and  quantity 
of  the  reduction  products  determined  in  each  case.  It  turned 
out  that  the  emphasized  differences  in  the  results  disappeared 
and  that,  with  an  equal  potential  of  all  cathodes,  similar  yields 
of  azoxybenzene  and  aniline  and  traces  of  azobenzene  resulted. 
The  cathodes  were  of  platinum,  copper,  copper  and  copper 
powder,  tin,  platinum  with  addition  of  stannous  hydroxide, 
zinc,  platinum  with  addition  of  zinc  hydroxide,  lead,  platinum 
with  addition  of  lead  hydroxide,  and  nickel.  The  yields  of 
azoxybenzene  varied  from  41-65%;  of  aniline  23-53%. 

Considering  the  trifling  quantity  of  the  product  started 
with  which,  had  to  be  chosen  in  order  to  at  all  carry  out  the 
experiments,  and  considering  the  difficulty  with  which  an 
accurate  quantitative  separation  and  determination  of  the 
reduction  products  could  be  carried  out,  the  proposition  that 
can  be  laid  down  as  a  sure  result  of  the  above  is  that  the  cathode 
potential  is  the  measure  for  the  reduction  energy  for  nitrobenzene 
when  a  2%  sodium-hydroxide  solution  is  employed  as  electrolyte. 

Another  investigation  may  here  be  mentioned  which— 
chiefly  carried  out  with  nitro-bodies — contains  ideas  which 
become  of  general  importance  and  can  perhaps  furnish  a  new 
physicochemical  method  for  determining  constitutions. 

Panchaud  de  Bottens *  has  determined  the  drop  in  potential 

1  Ztschr.  f.  Elektrochemie  8,  305,  332  (1902). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        153T 

to  which  a  hydrogen  electrode  is  subject  on  the  addition  of  bodies 
of  the  aromatic  series.  Tnese  "  depolarizing  values/'  when 
measured  under  exactly  similar  circumstances,  are  a  function 
of  the  chemical  nature  of  the  depolarizer  and  are  closely  related 
to  their  composition  and  constitution.  It  might  be  of  particular 
interest  to  choose  an  oxygen  electrode  in  place  of  a  hydrogen 
electrode,  since  perhaps  all  organic  substances  show  a  depolariz- 
ing value  when  measured  by  the  former.  The  results  are  tne 
following : 

The  depolarization  of  a  hydrogen  electrode  in  the  presence  of 
a  reducible  body  was  investigated,  fifty-three  aromatic  bodies 
being  thus  examined:  Nitroso-,  nitro-  and  nitrosamine-, 
isodiazo--  and  diazonium-bodies.  The  investigation  of  the  depo- 
larization was  made  by  taking  into  consideration  its  course  in 
time  and  in  connection  with  the  concentration. 

1.  The  reduction  energy  of  hydrogen  at  platinized  platinum 
electrodes  can  be  given  in  comparison  with  reducible  bodies  as 
"  depolarization  value  "  in  volts. 

2.  Analogously  constituted  bodies  have  analogous  depolar- 
ization values. 

3.  Different  groups  of  depolarization  values  correspond  to 
differently  constituted  groups  of  bodies. 

4.  The  absolute  values  of  the   classes  of  bodies  investi- 
gated in  acid  solution  (n/i  H2S04  or  n/i  CH3COOH)  are  the  fol- 
lowing : 

a.  Nitroso-compounds  =  0.64  -0.5  volt, 

b.  Mononitro-compounds  =  0.33  —  0.23  volt, 

c.  Nitrosamines  and  isodiazohydrates  =  0.16  — 0.09  voRfr, 

d.  Diazonium  compounds  =  0.47  — 0.37  volt, 

e.  Isodiazotates,   normal  diazo-compounds,   do  not  de- 

polarize. 

5.  Regular  laws  have  not  resulted  in  the  case  of  isomers 
within  a  group. 

6.  In  acid  solution,  in  the  case  of  isomers  of  nitro-disubsti- 
tution  products,  the  ortho-position  proved  to  be  the  one  which, 
depolarized  the  hydrogen  electrode  the  most. 


154         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

7.  The  method  for  the  determination  of  the  depolarization 
value  shows  in  the  case  of  the  two  investigated  isodiazohydrates 
(isodiazobenzenehydrate  and  p-nitroisodiazobenzenehydrate) 
that  they  belong  to  the  nitrosamines. 

III.  Presentation  of  the  Reduction  Phases  of  Nitrobenzene. 

An  idea  of  the  electrolytic  behavior  of  nitrobenzene  is  best 
obtained  by  the  use  of  the  reduction  scheme,  by  carrying  out 
the  experiments  according  to  the  chief  products  occurring  in 
the  reductions.  For  after  the  first  observations  of  Kendall/ 
Elbs,2  Haussermann,3  and  Lob,4 — who  all  taught  and  showed 
the  variety  of  obtainable  products  that  it  is  possible  to  bring 
about  electrolytically  at  almost  every  reduction  stage — a  desire 
predominated  to  find  out  the  conditions  which  make  possible 
and  favor  the  preponderating  formation  of  a  certain  substance. 
The  primary  reduction  products  are  nitrosobenzene,  phenylhy- 
droxylamine  and  aniline.  Secondary  substances,  i.e.  those 
produced  by  chemical  action,  are  azoxybenzene  and  azobenzene, 
,  which  in  turn  can  give  hydrazobenzene  or  benzidine  and  aniline. 
Phenylhydroxylamine  can  pass  into  amidophenol  and  also 
undergo  other  rearrangements  and  condensations.  The  pos- 
sibility of  causing  at  will  certain  phases  to  yield  the  chief  prod- 
ucts of  reduction  is  of  great  importance  for  the  manufacturing 
and  technical  side  of  the  electrolysis  of  nitrobenzene.  The 
following  is  known  concerning  the  formation  of  the  separate 
reduction  stages: 

Nitrosobenzene. — It  is  natural  that  so  good  a  depolarizer  as 
nitrosobenzene  is  at  the  cathode  cannot  be  separated  as  such 
under  the  conditions  of  a  continuous  reduction.  Haber,5  by 
adding  a-naphthol  and  hydro xylamine  to  the  electrolyte  in 
alkaline  solution,  could,  however,  prove  the  presence  of  nitro- 
sobenzene in  the  form  of  its  characteristic  condensation  product, 

1  D.  R.  P  No.  21131  (1883). 

2Chem.  Ztg.  17,209  (1893). 

3  Ibid.,  129,209  (1893). 

<Ztschr.  f.  Elektrochemie  3,  471  (1897). 

5  Ibid.  4,  511  (1898). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        155 

benzeneazo-a-naphthol,  C6H5N=NCioH6OH;  similarly  in  acid 
solution  by  adding  hydroxylamine  and  a-naphthylamine, 
as  benzeneazo-a-naphthylamine,  CeH5N  =NCi0H6NH2.  These 
methods  of  preparation  of  both  dyes  are,  of  course,  only  of 
theoretical  interest. 

Phenylhydroxylamine. — Haber  1  electrolyzed,  a  solution  of 
10  g.  nitrobenzene  in  215  cc.  glacial  acetic  acid,  which  was 
diluted  to  425  cc.,  in  an  earthenware  cylinder,  and  employed 
a  platinum  cathode  of  25  sq.  cm.  surface  (one  side)  and  a  current 
density  of  1.5,  later  1,  amp.  For  this  latter  a  voltage  of  80  was 
at  first  necessary,  on  account  of  the  low  conductivity  of  the 
solution.  The  temperature  was  kept  below  20°  by  artificial 
cooling.  After  six  to  eight  hours  the  electrolyte  contained 
large  quantities  of  phenylhydroxylamine.  The  same  investi- 
gator 2  in  conjunction  with  Schmidt,  on  electrolyzing  nitro- 
benzene in  alcoholic  ammonia  with  addition  of  sal-ammoniac, 
isolated  phenylhydroxylamine,  besides  azoxybenzene  and  a 
little  azobenzene. 

C.  F.  Boehringer  &  Sohne  and  C.  Messinger  3  obtain  phenyl- 
hydroxylamine in  a  peculiar  manner.  A  lead  electrode  and  an 
earthenware  diaphragm  are  placed  in  a  container,  and  a  porous 
carbon  cell  in -the  earthenware  diaphragm.  The  lead  electrode 
serves  as  anode,  the  carbon  cell  as  cathode.  The  outer  container 
and  the  earthenware  cell  are  filled  with  a  30%  sulphuric 
acid  serving  as  electrolyte;  nitrobenzene  is  forced  through  the 
carbon  cell  towards  the  earthenware  cell  under  a  pressure  of 
0.5  atmosphere.  If  the  solution  is  now  electrolyzed  at  a  current 
density  of  2  amp.  per  square  decimeter  and  a  temperature  up  to 
25°,  phenylhydroxylamine  is  formed  as  end-product,  since  at 
this  low  temperature  and  in  the  dilute  acid  no  molecular  rear- 
rangement into  amidophenol  can  take  place. 

Kolecular  Rearrangement  and  Condensation  Products  of 
Phenylhydroxylamine. — The  difficulty  and  subtilty  of  the 
electrolytic  preparation  of  phenylhydroxylamine  depends  upon 

1  Ztschr.  f.  Elektrochemie  4,  511  (1898). 

2  Ztschr.  f.  phys.  Chem.  32,  283  (1900). 

3  D.  R.  P.  No.  10905  (1898). 


156         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

the  great  reactivity  of  the  body,  which  reactivity  exposes  it, 
even  during  the  electrolysis,  to  further  reactions.  In  alkaline 
solution  it  is  chiefly  the  condensation  of  phenylhydroxylamine 
with  its  predecessor  in  the  reduction,  nitrosobenzene,  to  azoxy- 
benzene;  or  in  alcoholic-alkaline  solution  the  condensation  of  two 
molecules  to  azobenzene.  In  acid  solution  the  rearrangement 
phenomena  caused  by  the  acids  are  chiefly  important.  Owing  to 
the  dependence  of  the  rearrangement  velocity  upon  the  acid 
concentration,  concentrated  acids  are  best  suited  for  the  pur- 
pose. The  nature  of  the  acid  is  often  decisive  for  the 
rearrangement  products. 

Amidophenol. — On  reducing  nitrobenzene  in  concentrated 
sulphuric  acid,  Noyes  and  Clement1  obtained  p-amido- 
phenolsulphonic  acid.  Gattermann  and  Koppert,2  by  'using 
nitrobenzenesulphonic  acid  in  tolerably  concentrated  sul- 
phuric acid,  got  p-amidophenol  sulphate.  Gattermann,3  on 
varying  the  experimental  conditions,  also  employing  con- 
centrated sulphuric  acid,  obtained  para-amidophenol  directly 
from  nitrobenzene.  He  explains  the  latter ?s  formation  by 
assuming  the  intermediate  production  of  phenylhydroxyl- 
amine, which  in  further  reduction  rearranges  itself  into  the 
end-product. 

C6H5N02  +  2H2  =  C6H5NHOH  +  H20, 
C6H5NH(OH)  =  NH2C6H4OH. 

Some   o-amidophenol  is  formed  besides  the   p-compound. 

Chlor  aniline. — Lob  4  has  found  that  p-  and  o-chl  or  aniline 
are  obtained  by  the  electrolytic  reduction  of  nitrobenzene 
suspended  in  fuming  hydrochloric  acid,  nitrobenzene  dissolved 
in  alcoholic  hydrochloric  acid,  and  nitrobenzene  dissolved  in 
mixtures  of  hydrochloric  and  acetic  acids.  With  hydrobromic 
acid  the  corresponding  bromanilines  are  formed. 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  26,  990  (1893). 
2Chem.  Ztg.  17,210  (1893). 


3  Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1844  (1893). 

4  Ztschr.  f .  Elektrochemie  3,  46  (1896) ;  Ber.  d.  deutsch.  chem.  Gesellsch. 
29,  1894  (1896). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        157 
The  reaction  takes  place  as  shown  in  the  following  equations: 


2. 

HHC1= 


3.  C6H5NHC1=0~C1C6H4NH2. 


The  phenylchloramine  formed  by  the  action  of  hydro- 
chloric acid  on  phenylhydroxylamine  changes  by  molecular 
rearrangement  into  o-  and  p-chlor  aniline. 

Condensation  Products  with  Aldehydes.  —  Gattermann1  has 
obtained  direct  proof  of  the  intermediate  formation  of  phenyl- 
hydroxylamine in  the  preparation  of  amidophenol  by  adding 
benzaldehyde  to  the  solution  at  the  beginning  of  the  elec- 
trolysis. He  was  thus  able  to  isolate  a  condensation  product 
of  phenylhydroxylamine  with  benzaldehyde.  In  this  way  he 
obtained  from  nitrobenzene  benzylidene-phenylhydroxylamine, 

/0\ 


The  presence  of  formaldehyde  in  the  electrolytic  reduction 
of  nitro-compounds  produces  an  effect  entirely  different 
from  that  caused  by  the  addition  of  benzaldehyde.  The 
phenomena  occurring  in  this  case  have  been  thoroughly 
investigated  by  Lob.2 

The  fundamental  object  of  his  researches  differs  from 
that  of  Gattermann,  in  that  Lob  undertakes  to  establish 
the  separate  phases  of  the  reduction  of  the  nitro-group. 
This  he  accomplishes  by  the  addition  of  formaldehyde  to 
the  electrolyte  under  varying  conditions,  and  as  a  result  the 
intermediate  products,  at  the  moment  of  their  formation,  com- 
bine with  formaldehyde,  producing  condensation  compounds 
which  do  not  undergo  further  decomposition.  By  regulat- 
ing the  potential  or  density  of  the  current  the  reaction  can  at 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  3040  (1896). 

2  Ztschr.  f.  Elektrochemie  4,  428  (1898). 


158         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

will  be  checked  at  a  perfectly  definite  phase  of  the  reduc- 
tion. 

In  the  electrolysis  of  nitrobenzene  by  this  method  there 
were  formed: 

1.  p-Anhydrohydroxylaminebenzyl  alcohol, 


which  may  also  be  directly  prepared  by  the  action  of  for- 
maldehyde on  phenylhydroxylamine. 

2.  Methylenedi-p-anhydroamidobenzyl  alcohol, 


\NH-C6I 

a  reaction  product  of  formaldehyde  and  aniline. 
3.  Anhydro-p-amidobenzyl  alcohol,1 


[/CH 
C6H4<(    | 
\NH 


which  can  be  likewise  obtained  by  the  action  of  formaldehyde 
upon  aniline. 

Azoxybenzene.  —  This  substance  was  recognized  some  time 
ago  in  the  investigations  of  Elbs,2  Haussermann,3  Straub,4  etc., 
as  one  of  the  reduction  products  occurring  both  in  the  acid 
and  alkaline  electrolytic  reduction  of  nitrobenzene.  Bam- 
berger  and  Haber  then  explained  its  formation  by  the  con- 
densation of  phenylhydroxylamine  and  nitrosobenzene.  Lob,5 
by  electrolyzing  nitrobenzene  suspended  in  dilute  aqueous- 
alkaline  or  alkaline-salt  solutions  at  unattackable  cathodes 


1  Ber.  d.  deutsch  chem.  Gesellsch.  31,  2037  (1898). 

2  Chem.  Ztg.  17,  209  (1893). 


3  Ibid.,  129  (1893). 
*D.  R.  P.  No.  79731  (1894). 

6Ztschr.  f.  Elektrochemie  7,  335  (1900);    Ztschr.  f.  phys.  Chem.  34,  641 
(1900). 


THE  ELECTROLYSIS  OF   AROMATIC  COMPOUNDS.        159 

(platinum,  nickel,  mercury),  succeeded  in  finding  a  method 
which  gives  a  good  material-  and  current-yield  of  azoxyben- 
zene  almost  free  from  other  reduction  products.  In  this 
case  the  unattackable  cathode  plays  a  leading  part,  aside 
from  the  use  of  aqueous  electrolytes.  The  choice  of  attack- 
able cathodes  modifies  the  process  very  considerably,  the 
nature  of  the  metal  producing  individual  effects. 

Azobenzene.  —  Alcoholic-alkaline  solutions  act  differently 
from  aqueous-alkaline  electrolytes.  Even  if  unattackable 
electrodes  are  employed  with  the  former,  the  process  can  be 
regulated  so  as  to  give  very  good  yields  of  azobenzene.  This 
was  demonstrated  by  Elbs  and  Kopp.1  Two  concurrent 
processes  determine  presumably  the  azobenzene  formation, 
firstly,  the  splitting  off  of  water  from  two  molecules  of  phenyl- 
hydroxylamine  produced  by  the  influence  of  the  alcoholic- 
alkaline  solution;  secondly,  the  reaction  of  hydrazobenzene 
(resulting  from  the  azoxybenzene  formed  secondarily)  with 
unchanged  nitrobenzene  or  nitrosobenzene.  That  the  latter 
reaction  occurs  is  shown  by  the  fact  that,  if  the  electrolysis 
is  prematurely  interrupted,  azoxybenzene  and  azobenzene  and 
hydrazobenzene  are  always  present.  When  alcoholic  electrolytes 
were  employed  it  proved  advantageous  to  substitute  for  the 
free  alkali  sodium  acetate  which,  on  account  of  its  easy  solubility 
in  alcohol,  its  good  conductivity  and  trifling  action  on  the 
diaphragm,  possesses  considerable  advantages  over  sodium 
hydroxide.  These  processes  are  not  technically  valuable  on 
account  of  the  employment  of  alcohol. 

Bayer  &  Co.2  seek  to  avoid  this  latter  inconvenience  by 
reducing  nitrobenzene,  suspended  in  aqueous  alkaline  or  alkali- 
salt  solutions,  in  the  presence  of  such  metallic  cathodes,  or  the 
addition  of  such  metallic  salts,  whose  oxides  are  soluble  in 
caustic  alkali, — for  instance  lead,  zinc,  tin,  or  their  salts.  The 
yields  of  azobenzene  obtained  by  this  method  are  said  to  be 


'Ztschr.  f.  Elektrochemie  5,  108  (1898);  D.  R.  P.  No.  100233,  100234 
(1898). 

2  D.  R.  P.  No.  121899  and  121900  (1899). 


160         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

almost  quantitative.  According  to  a  patent l  of  the  Farbwerke 
vorm.  Meister,  Lucius  &  Briining,  the  reduction  of  nitro- 
benzene to  azobenzene  can  also  be  accomplished  in  aqueous- 
alkaline  solution,  if  the  electrolysis  is  carried  out  without  a 
diaphragm  but  with  a  large  cathode  and  small  anode  and  at  a 
high  temperature  (105°-115°). 

Hydrazobenzene. — In  hydrazobenzene  we  have  a  reduction 
product  of  nitrobenzene  which  is  next  in  importance  to  aniline, 
being  employed  in  large  quantities  in  the  manufacture  of  benzi- 
dine.  Its  electrolytic  preparation  exceeds  in  importance  that 
of  aniline;  the  purely  chemical  method  of  preparing  benzidine 
is  more  complicated,  less  smooth,  and  gives  poorer  yields  than 
that  of  aniline,  so  that  great  exertions  have  been  put  forth  to 
make  the  electrolytic  manufacture  of  the  former  practical. 
According  to  Straub,2  hydrazobenzene  is  obtained  from  nitro- 
benzene in  alcoholic-alkaline  solution  by  choosing  such  suitable 
conditions  of  solution  that  all  intermediate  products  are  kept  in 
solution,  but  the  difficultly  soluble  hydrazobenzene  is  precipi- 
tated, thus  withdrawing  it  from  the  further  action  of  the  current. 

Both  azoxybenzene  and  azobenzene  are  converted,  by 
suitable  reduction,  into  hydrazobenzene.  Both  mehods  have 
already  been  followed.  Elbs  and  Kopp  3  work  in  alcoholic- 
alkaline  solution  and  obtain  hydrazobenzene  from  nitrobenzene 
in  one  process,  by  way  of  azoxy-  and  azobenzene.  They  obtain 
excellent  yields,  but  by  means  of  the  technically  impractical 
alcohol  method.  Bayer  &  "Co.  can  make  use  of  their  patented 
process 4  for  the  preparation  of  azobenzene  in  the  making  of 
hydrazobenzene,  by  continuing  the  electrical  reduction,  and 
obtain  good  yields  of  this  latter  substance. 

Lob  chooses  azoxybenzene  as  the  primary  substance  in  mak- 
ing hydrazobenzene.  This  method  corresponds  to  the  theo- 
retically demanded  reduction  course,  as  explained  for  the 
azoxybenzene  and  azobenzene  formation.  According  to  this 

1  D.  R.  P.  No.  141535  (1902). 

2  D.  R.  P.  No.  79731  (1894). 

3  Ztschr.  f.  Elektrochemie  5,  108  (1898). 
*  See  p.  159. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        161 

theory  azobenzene  is  a  condensation  product  of  hydrazobenzene 
and  nitro-  or  nitrosobenzene. 

Benzidine. — That  nitrobenzene,  by  electrolytical  reduction 
in  acid  solution,  can  directly  yield  benzidine,  was  first  proved  by 
Haussermann,1  who  used  sulphuric  acid.  Lob  2  later  proved  the 
same  to  be  true  for  hydrochloric-,  acetic-,  and  formic-acid 
electrolytes.  However,  several  reactions  predominate  in  this 
direct  acid  reduction,  which  prevent  the  carrying  out  of  the 
reaction  up  to  hydrazobenzene,  or  the  formation  of  benzidine. 
Phenylhydroxylamine  may  particularly  be  mentioned  in  this 
connection.  In  alcoholic-acid  solution  it  is  partly  rearranged 
to  amidophenol  or  its  ethers,  and  partly  reduced  to  aniline. 
Azoxybenzene,  in  acid  solution,  is  the  starting-point  in  the 
benzidine  formation;  however,  in  this  case,  the  combining 
velocity  of  nitrosobenzene  and  phenylhydroxylamine  is  not  very 
great,  so  that  the  latter  is  to  a  very  considerable  extent  subject 
to  the  more  rapidly  acting  influence  of  the  acid. 

Besides  azoxybenzene,  azobenzene  also  gives  hydrazo- 
benzene, as  already  mentioned,  e.g.  in  acid  solution  benzidine 
results.  Azobenzene,  however,  is  formed  only  in  very  small 
quantity. 

Lob,3  convinced  of  the  futility  of  thus  being  able  to  obtain 
a  good  yield  of  benzidine  by  a  direct  reduction  of  nitrobenzene 
in  acid  solution,  sought  to  carry  out  the  benzidine  process 
by  a  careful  realization  of  the  conditions  theoretically  required — 
primary  preparation  of  azoxy-  or  azobenzene  in  the  best  quan- 
titative yields,  i.e.  in  electrolytes,  containing  alkali  or  alkali- 
salt,  then  reducing  these  products  in  acid  solution.  Two 
processes  thus  resulted.  In  the  first  one  the  electrolytic 
reduction  was  carried  out  to  azobenzene  in  alcoholic-alkaline 
solution,  then  the  cathode  solution  was  acidified  with  sulphuric 
acid,  and  the  further  reduction  and  molecular  rearrangement 
combined  in  one  operation.  The  second  process,  which  was 

1  Chem.  Ztg.  77,  108  (1893). 

2  Ztschr.  f.  Elektrochemie  3,  471  (1897);  Ber.  d.  deutsch.  chem.  Gesellsch. 
29,  1894  (1896). 

3  Ztschr.  f.  Elektrochemie  7,  320,  333,  597  (1900-1901). 


162         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

worked  out  after  the  discovery  of  the  electrolytic  preparation 
of  azoxy benzene,  avoids  the  objection  of  adding  alcohol,  and 
takes  place  primarily  in  aqueous  alkali-  or  alkali-salt  solution 
at  unattackable  cathodes  with  azoxybenzene  as  the  result.  It 
appears  that  azoxybenzene,  in  sulphuric-acid  suspension,  is 
an  extremely  poor  depolarizer,  but  that  the  further  reduction 
takes  place  very  readily  in  a  hydrochloric-acid  electrolyte 
with  the  addition  of  a  trifling  quantity  of  stannous  chloride. 
Some  diphenyline  and  aniline  is  always  formed  besides  the 
benzidine,  the  aniline  probably  by  a  splitting  up  and  reduction 
of  hydrazobenzene  before  its  rearrangement. 

Aniline. — The  reactions  which  stand  in  the  way  of  the 
benzidine  preparation  are  also  of  a  disturbing  nature  in  the 
preparation  of  aniline  by  reduction  in  acid  solution;  espe- 
cially the  reactiveness  of  the  phenylhydroxylamine,  its  mo- 
lecular rearrangement  and  condensation,  at  first  hindered  the 
quantitative  further  reduction  to  aniline.  The  overcoming 
of  these  obstacles  was  brought  about  by  the  choice  of  suit- 
able cathode  metals.  Elbs  first  observed  the  influence  of 
the  cathode  metal  in  the  electrolytic  preparation  of  aniline. 
Lob  later  made  the  same  observation.  Elbs 1  found  that 
the  replacement  of  the  platinum  cathode  by  one  of  zinc  con- 
siderably favored  the  formation  of  aniline  from  nitrobenzene 
in  acid  solution;  later2  he  obtained  with  Silbermann  the 
same  successful  result  when  any  kind  of  a  cathode  was  used 
with  the  addition  of  a  zinc  salt.  The  same  investigators  have 
also  proved  in  previous  researches3  that,  under  similar  cir- 
cumstances, and  in  sulphuric  acid  solution,  much  more  aniline 
besides  amidophenol,  is  produced  at  a  lead  cathode  than  at  a 
platinum  cathode. 

Lob,4  independently  of  these  observations,  found  that 
an  almost  quantitative  yield  of  aniline  can  be  obtained  from 
nitrobenzene  in  hydrochloric-acid  solution  and  at  a  lead  cathode  ; 

1  Chem.  Ztg.  17,  209  (1893). 

2  Ztschr.    f.  Elektrochemie  7,  589  (1901). 

3  Ibid.  3,  472  (1896). 

4  Ibid.  4,  430  (1898). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        163 

later  Elbs  and  Silbermann1  also  obtained  90  per  cent  of  the 
theoretical  yield  of  aniline  with  the  aid  of  a  lead  cathode. 

We  are  indebted  to  C.  F.  Boehringer  &  Sohne2  for  the 
comprehensive  exploitation  of  the  influence  of , cathode  material 
in  the  preparation  of  aniline.  They  have  patented  the  results 
of  their  experiments.  The  importance  of  the  decisive  condi- 
tions of  the  experiments,  as  in  those  of  Elbs  and  Silbermann 
and  of  Lob,  lies  in  the  increase  of  the  reduction  velocity  of 
phenylhydroxylamine  to  aniline,  so  that  competing  rearrange- 
ment and  condensation  reactions  are  given  no  time  to  occur. 
Almost  quantitative  yields  of  aniline  are  obtained.  The  nature 
of  the  process  consists  in  reducing  the  nitrobenzene  in  acid 
solution,  or  suspension,  by  means  of  indifferent  electrodes  and 
with  the  addition  of  a  tin,  copper,  iron,  chromium,  lead,  or 
mercury  salt,  or  the  corresponding  metal  in  a  finely  divided  state. 

The  metal  employed,  or  the  corresponding  degree  of  quanti- 
valence  of  the  metal  ion,  is  regenerated  by  the  current,  depend- 
ing upon  the  greater  or  less  electrolytic  ismotic  pressure  of  the 
metal .  Cathodes  of  tin  can  also  be  employed  instead  of  the  tin  salt. 

It  may  be  mentioned  incidentally,  that  according  to  in- 
vestigations by  Holler3  a  strong  odor  of  phenylisocyanide, 
C6H5N  =  C,  occurs  in  the  electrolysis  of  nitrobenzene '  in  alco- 
holic-alkaline solution  and  without  a  diaphragm.  But  a  sepa- 
ration of  the  carbylamine  could  not  be  made.  Homologues 
of  nitrobenzene,  when  electrolyzed  under  analogous  condi- 
tions, also  yield  isonitrile. 

c.  Substitution  Products  of  Nitrobenzene. 
I.  General  Laws  governing  Substitution. 

The  reduction  scheme  sketched  by  Haber  for  the  reduction 
of  nitrobenzene  also  holds  true  for  the  substitution  products  of 
nitrobenzene  in  so  far  as  the  formation  of  their  reduction 
phases  can  be  coordinated  to  the  same  reduction,  condensation, 
or  molecular  rearrangement  processes.  But  the  decisive  influ- 

1  Ztschr.  f.  Elektrochemie  7,  589  (1901). 
2D.  R.  P.  No.  116942  (1899);  117007  (1900). 
3  Ztschr.  f.  Elektrochemie  5,  463  (1898). 


164         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

ence  of  the  substituents  manifests  itself  in  various  ways.  In 
the  first  place,  the  experimental  conditions  determined  for  the 
preparation  of  certain  reduction  stages  of  nitrobenzene  do  not 
obtain  for  its  derivatives,  at  least  only  in  a  limited  manner. 
The  position  and  nature  of  the  substituents  also  often  hinder 
the  preparation  of  single  phases.  In  other  words:  the  reac- 
tion velocity  with  which  reduction,  condensation,  and  rear- 
rangement take  place  is  fundamentally  influenced. 

Nevertheless  some  reactions  are  known  which  possess  a 
certain  general  applicability.  This  is  true  of  Gattermann's 
reduction  in  concentrated  sulphuric  acid,  which  gives  mostly 
amidophenols,  if  the  ortho-  or  para-position  is  unoccupied. 
Only  p-nitrotoluene  and  the  nitroaldehydes  form  exceptions, 
which  will  be  discussed. 

The  reduction  in  alkaline  solution  likewise  leads  almost 
always  to  azo-  and  azoxy-bodies,  or  hydrazo-bodies.  The  laws 
here  predominating  have  chiefly  been  investigated  by  Elbs  1 
and  his  pupils.  The  exceptions  to  the  rule,  the  occurrence  of 
amines  in  place  of  azo-  and  azoxy-compounds  were  clearly 
explained  by  Elbs.  P-Nitraniline,  electrolyzed  under  the  same 
conditions  which  give  m-diamidobenzene  from  m-nitraniline, 
yields  only  p-phenylenediamine.  This  phenomenon  is  based 
on  the  fact  that  p-nitraniline  readily  yields  quinone  derivatives, 
but  m-nitraniline  does  not.  Thus  the  primarily  produced 
p-amidophenylhydroxylamine-- is  changed  to  quinonediimide, 
which  on  further  reduction  can  yield  only  a  diamine: 

/NHOH  JSFH 

I.  C6H4<  ->C6H4f        +H20. 

\NH2 


/NH2 

nf^   TT  v  i   TT  f^  TT  y' 

.    UG^U^  +  AJ-2  — ^  v^6-H-4\ 

^NH  \NH2 

Or  this  rearrangement  occurs  already  in  the  nitroso-phase,  which 
leads  to  the  same  result: 

/NO 


1  Ztschr.  f.  Elektrochemie  7,  133,  141  (1900). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        165 

Since  the  tendency  to  form  quinone  derivatives  is  lacking 
in  m-nitraniline,  the  nitroso-  and  hydroxylamine  phase  can 
unite  normally  to  the  azo-body. 

For  the  same  reason  perhaps  the  exclusive  formation  of 
o-  arid  p-amidophenol  occurs: 

NO  .NOH 


)H 

/NHOH  .NOH 

or  C6H4<  ->C6H4C  +H20. 

XOH  ^0 

These  quinone  derivatives,  by  further  reduction,  can  pro- 
duce only  amidophenols.  If  the  quinone  formation  is  prevented 
from  taking  place,  for  instance  by  esterifying  the  hydroxyl- 
group,  the  normal  reaction  to  azoxy-bodies  occurs,  o-  and  p- 
Nitroanisol  pass  smoothly  into  azoxy-  or  azo-derivatives.  The 
acylizing  of  the  amido-group  in  the  case  of  o-  and  p-nitroamines 
hinders  likewise  the  quinone,  and  therewith  the  amine,  forma- 
tion. The  azoxy-body  is  smoothly  formed,  thus: 
NO  HOHN  „ 

p,  TT  .  r<  TT 

\    6    5  ceH5 

XCOC6H5      C6H5CO 


-64-—       -64- 

C6H5CCK  XCOC6H5  +  H20. 

But  the   alkylization   does  not  prevent  the  formation  of 
quinone  and  therefore  the  reduction  to  the  amido-phase  : 

/NO 

C6H4 


NHOH  ,NOH 

or  C6H4  -^C6H4  +H20. 


Elbs  sums  up  in  the  following  manner  the  rules  which  apply 
to  the  electrochemical  reduction  of  aromatic  mononitro-bodies 
in  alkaline  solution.  Hereby  it  must  be  taken  into  considera- 
tion that  the  primarily  formed  azoxy-body,  under  the  condi- 
tions chosen  by  Elbs,  leads  to  the  azo-body. 


166         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

1.  Nitrobenzene  and  its  homologues  give  azo-bodies;  amines 
do  not  occur,  or  only  in  traces. 

2.  Halogenized  nitrobenzenes   and  their  homologues  yield 
azo-compounds;    difficulties  occasionally  occurring  are  caused 
by  the  alkaline  cathode  fluid  attacking  the  halogen  made  mobile 
by  the  nitro-group,  or  inversely  the  nitro-group  made  mobile  by 
several  halogen  atoms. 

3.  Nitrobenzene-m-sulphoriic  acid  arid  its  homologues  give 
azo-bodies. 

4.  Nitrobenzenecarboxylic  acids  yield  azo-compounds,  but 
only  the  o-acids  behave  differently.1 

5.  m-  and  p-Nitroacid-nitriles  yield  azo-bodies,  with  or  with- 
out a  partial  saponification,  depending  upon  the  conditions  of 
the  experiment. 

6.  m-Nitraniline  and  its  homologues  give  azo-bodies,  but 
o-and  p-nitraniline  and  its  homologues,  on  the  contrary,  give 
diamines. 

The  same  rule  obtains  for  the  secondary  and  tertiary  amines 
derived  from  the  three  nitranilines. 

7.  Acylized  nitranilines  (acidnitroamides)  and  their  homo- 
logues give   azo-bodies,   no  matter  which  position  the   nitro- 
group  occupies  in  regard  to  the    acylized  amido-group.     The 
cathode    fluid    must    be    kept    approximately   neutral   during 
reduction,    otherwise   the    acid   amides   are   saponified  if  the 
solution  becomes  considerably  alkaline. 

8.  o-  and  p-Nitrophenols  give  amidophenols. 

9.  Nitrophenol   ethers    give   azo-bodies,    no   matter    what 
position  the  nitro-group  occupies. 

These  rules  do  not  hold  true  for  dinitro-bodies. 

The  experiences  gained  in  the  electrolysis  of  nitrobenzene 
concerning  the  influences  of  the  cathode  material  have  also 
obtained  in  great  measure,  with  the  substituted  nitrohydro- 
carbons.  The  general  result  can  be  summed  up  in  the  state- 
ment that  at  unattackable  cathodes,  such  as  platinum,  nickel, 


Lob,  Ztschr.  f.  Elektrochemie  2,  532  (1896). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        167 

and  mercury,  in  aqueous-alkaline  solution  azoxy-bodies l  are 
produced,  and  at  attackable  cathodes,  such  as  lead  or  copper, 
azo-,  hydrazo-,2  and  even  amido-compounds  are  formed.  The 
latter  are  obtained  by  the  method  of  C.  F.  Bohringer  &  Sohne,3 
using  a  copper  cathode,  or  an  unattackable  cathode  with 
addition  of  copper  powder.  o-Toluidine,  m-phenylenediamine 
from  m-nitraniline,  and  a-naphthylamine,  in  addition  to  ani- 
line, were  prepared  in  good  yields  by  this  method. 

In  alcoholic  solution  this  difference  does  not  occur  so  dis- 
tinctly; it  is  also  easy  to  reduce  to  the  hydrazo-phase  at 
unattackable  electrodes. 

The  influence  of  the  cathode  metal  is  much  more  mani- 
fest when  acid  electrolytes  are  employed  than  in  alkaline 
reduction.  In  alkaline  solution  at  copper  electrodes,  if  we 
except  the  last-mentioned  process,  the  rapidly  occurring  con- 
densation of  the  first  reduction  phases — of  the  nitroso-  and 
hydroxylamine  body — always  leads  immediately  to  the  azoxy- 
body  and  makes  this  appear  to  be  the  typical  product  of  the 
alkaline  reduction,  which  can  in  turn  be  further  reduced.  In 
acid  solution  this  condensation  takes  place  so  slowly  that 
the  molecular  rearrangement  of  the  hydroxylamine  and  its 
further  reduction  to  amine  has  time  to  take  place  alongside 
the  formation  of  the  azoxy-body  and  the  reduction  of  the 
latter  to  the  hydrozo-compound  or  benzidine.4 

The  increased  reactivity  of  the  whole  molecule  or  single 
groups,  which  is  often  associated  with  the  entrance  of  nitro- 
groups,  is  also  apparent  in  the  capability  of  some  nitro-bodies  to 
be  relatively  easily  oxidized.  The  little  that  is  known  is  ap- 
pended to  the  description  of  the  behavior  of  the  individual 
members.  The  characteristic  features  of  the  oxidation  processes 
in  question  have  been  explained  in  the  first  chapter  (p.  27 
et  seq.). 

1  Ztschr.  f.  Elektrochemie  7,  335  (1900). 

2  D.  R.  P.  No.  121899  and  121900  (1899). 
8  D.  R.  P.  No.  130742  (1901). 

*Cf.  Haussermann,  Chem.  Ztg.  17,  209  (1893). 


168        ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 
II.  Homologues  of  Nitrobenzene. 

NlTROTOLUENES. 

o-Nitrotoluene  behaves  very  much  like  nitrobenzene.  It 
gives  o-tolidine  and  a  little  o-toluidine  in  sulphuric-  or  hydro- 
chloric-acid solution  (Haussermann).1  In  concentrated  sul- 
phuric acid  Gattermann  and  Abresch2  obtained  o-amido-m-cresol  : 


Benzylidene-o-tolylhydroxylamine,3  corresponding  to  the 
benzylidenephenylhydroxylamine,  is  produced  in  the  presence 
of  benzaldehyde. 

According  to  the  experiments  of  Haussermann,4  Elbs  and 
Kopp,5  and  Lob,6  azotoluene  is  primarily  and  almost  exclusively 
produced  in  alkaline-alcoholic  solution,  and,  on  further  reduc- 
tion, hydrazotoluene.  The  same  results  can  also  be  obtained 
as  shown  in  the  process  of  the  above-mentioned  patents  for 
the  preparation  of  azo-  and  hydrazobenzene.  If  electrolyzed  in 
alkaline-aqueous  suspension,  there  is  formed  on  the  contrary, 
azoxytoluene  (process  of  Lob  7;,  which  can  be  converted  into 
o-tolidine  in  a  hydrochloric-acid  electrolyte  with  tin  cathodes,  or 
at  an  unattackable  cathode  with  additions  of  stannous  chloride. 

A  solution  of  o-nitrotoluene  in  a  mixture  of  sulphuric  and 
acetic  acids,  if  oxidized  at  a  platinum  anode,  gives  a  poor  yield 
(about  30  per  cent.)  of  o-nitrobenzyl  alcohol  (Pierron8). 

m-Nitrotoluene,  if  electrolyzed  in  concentrated  sulphuric 
acid,  passes  into  m-amido-o-cresol  (Gattermann  and  Heider9). 
If  benzaldehyde  is  present,  benzylidene-m-tolylhydroxylamine 
forms  (Gattermann  10). 

1  Chem.  Ztg.  17,  209  (1893). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  1929  (1894). 

3  Ibid.  29,  3040  (1896). 

*  Chem.  Ztg.  17,  129  (1893). 

6  Ztschr.    f.  Elektrochemie  5,  110  (1896), 

6  Ibid.  5,  459  (1899). 

7  Ibid.  7,  335  (1900). 

8  Bull.  Soc.  Chim.  [3]  25,  852  (1901). 

9  Ber.  d.    deutsch.  chem.  Gesellsch.  27,  1930  (1894). 

10  Ibid.  29,  3040  (1896). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        169 

Electrolyzed  in  alcoholic-alkaline  solution,  according  to 
the  directions  of  Elbs,  m-azotoluene  is  almost  quantitatively 
produced;  the  further  current  action  gives  m-hydrazotoluene 
(Rohde  !)• 

Lob  and  Schmitt2  electrolyzed  m-nitrotoluene  in  alkaline- 
aqueous  suspension,  employing  various  cathode  metals  in 
order  to  determine  their  influence.  The  other  conditions  of 
the  experiments  were  the  same.  m-Azoxytoluene,  which  is  to 
a  small  extent  converted  into  hydrazotoluene,  and  m-toluidine 
are  produced.  The  yields  vary,  depending  upon  the  nature  of 
the  cathode:  the  reduction  was  weakest  at  nickel  cathodes,  i.e., 
it  hardly  passed  beyond  the  azoxy-phase ;  at  zinc,  copper,  and 
copper  in  the  presence  of  copper  powder,  the  yield  of  amine 
increases  in  the  given  series  of  the  metals,  while  that  of 
azoxytoluene  decreases.  The  following  table  shows  these  rela- 
tions. Five  grams  m-nitrotoluene  gave : 


iTield  in  Grams  o 

r 

Azoxytoluene. 

Hydrazo- 
toluene. 

Toluidine. 

\ickel 

2  47 

0   36 

0.46 

Zinc 

2  42 

0.29 

0.56 

Copper 

1  83 

0  24 

1   16 

Copper  and  copper  powder  

1.38 

0.17 

1.68 

Pierron,3  by  oxidizing  electrolytically  m-nitrotoluene  under 
the  conditions  chosen  for  the  o-nitrotoluene,  obtained  about 
20  per  cent  m-nitrobenzaldehyde. 

p-Nitrotoluene. — In  dilute  sulphuric-acid  solution,  Hausser- 
mann 4  obtained  p-toluidine  as  the  chief  product ;  Gatter- 
mann  and  Koppert,5  by  reducing  in  concentrated  sulphuric 


1  Ztschr.    f.  Elektrochemie  5,  322  (1899). 

2  Ibid.  10,  756  (1904). 

3  Bull.  soc.  chim.  [3]  25,  852  (1901). 
4Chem.  Ztg.  17,  209  (1893). 


6Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1852,  2810  (1893);   D.  R.  P.  No. 
75261  (1893). 


170         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

acid,  found  a  process  varying  from  the  normal  reaction,  since 
the  amidophenol  formation  cannot  occur  when  the  p-position 
is  occupied.  The  reduction  leads  to  nitroamido-o-benzyl 
alcohol,  a  substance  evidently  produced  by  condensation  of  the 
intermediately  occurring  p-amidobenzyl  alcohol  with  nitrotoluene 
and  having  the  formula 

/CH2v  /CH3 

C6H4<          XC6H3<( 

XNH2  XN02 

On  further  electrolytic  reduction  this  compound  is  converted 
into  diamidophenyltolylmethane. 

If  benzaldehyde  is  added  to  the  sulphuric  acid,  benzyl- 
idene-p-tolylhydroxylamine  is  normally  produced  (Gatter- 
mann  x). 

C.  F.  Boehringer  &  Sohne  2  found  that,  if  cathodes  of 
tin,  copper,  lead,  iron,  chromium,  or  mercury  are  chosen,  or 
the  salts  of  these  metals  at  unattackable  cathodes  are  added 
to  the  electrolytes,  p-nitrotoluene  in  a  hydrochloric-acid  elec- 
trolyte is  smoothly  converted  into  p-toluidine. 

Lob3  found  that,  if  p-nitrotoluene,  in  alcoholic-hydro- 
chloric acid  solution  or  aqueous-hydrochloric  acid  suspension 
is  electrolytically  reduced,  preferably  at  lead  cathodes  in  the 
presence  of  formaldehyde,  there  are  formed  p-dimethyltolui- 
dine  and  a  condensation  product  of  p-toluidine  and  formalde- 
hyde. According  to  Goecke,4  this  has  the  composition 

(CH3C6H4NCH2)X, 

and  possesses  perhaps  the  constitution  of  a  trimethylenetritol- 
uidine,  which,  on  further  reduction,  yields  p-dimethyltoluidine  : 

/CH2—  NC6H4CH3 
CH3C6H4N<  >CH2 

X— 


NC6H4CH3 
/CH3 

=  CH3C6H4N<         +  2CH3C6H4NH2  +  CH20. 
XCH3 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  3040  (1893). 
2D.  R.  P.  No.  116942  (1899);    117007  (1900). 
3  Ztschr.  f.  Elektrochemie  4,  428  (1898). 


4  Ibid.  9,470,  (19C3). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        171 


The  excess  of  formaldehyde  present  in  the  liquid  again 
acts  on  the  toluidine,  so  that  a  mixture  of  dimethyltoluidine 
and  trimethylenetritoluidine  results. 

In  alcoholic-alkaline  solution  Elbs,1  Elbs  and  Kopp,2  and 
Lob 3  obtained  p-azotoluene.  If  the  electrolysis  is  prema- 
turely interrupted,  the  electrolyte  contains  large  quantities 
of  p-azoxy toluene ;  on  prolonged  electrolysis  p-hydrazotoluene 
is  quantitatively  produced,  according  to  the  process  of  Elbs. 

Lob  and  Schmitt4  investigated  the  behavior  of  p-nitro- 
toluene  in  alkaline-aqueous  suspension  at  different  cathodes. 
The  result  is  similar  to  that  obtained  in  the  case  of  m-nitro- 
toluene,  but  the  azoxy-body  was  always  contaminated  with 
some  azo-compound.  Five  grams  p-nitrotoluene  gave  the 
following: 


i 

field  in  Grams  of 

Electrode. 

Azotoluene 
+ 
Azoxytoluene 

Hydrazo- 
toluerie. 

Toluidine. 

Nickel  

2.66 

0.19 

0.67 

Zinc      

2.52 

0.15 

0.88 

Copper     

2.10 

0.11 

1.34 

Copper  and  copper  powder  

1.70 

0.05 

1.89 

If  the  current  yields  obtained  under  similar  conditions  from 
m-  and  p-nitrotoluene  are  compared  with  one  another,  it  is 
found  that  the  p-compound  is  more  easily  reducible  than  the 
m-body.  The  influence  of  the  position  of  the  methyl  group  is 
thus  shown  both  in  the  chemical  result  and  the  resistance 
towards  reducing  agents. 

Elbs,5  by  electrolytically  oxidizing  p-nitrotoluene  in  a 
mixture  of  concentrated  acetic  and  sulphuric  acids  at  a  large 
platinum  anode,  obtained  p-nitrobenzyl  alcohol, — current  yield 
30  per  cent,  material  yield  40  per  cent. 

1  Chem.  Ztg.  17,  209  (1893);  Ztschr.  f.  Elektrochemie,  4,  499  (1898). 

2  Ztschr.    f.  Elektrochemie  5,  110  (1898). 

3  Ibid.  5,  459  (1899). 

4  Ibid.  10,  756  (1904). 
6  Ibid.  2,522  (1896). 


172         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

If  the  electrolysis  is  carried  out  in  80%  sulphuric  acid, 
both  p-nitrobenzaldehyde  and  the  alcohol  are  obtained  (Lab- 
hardt  and  Zschoche1). 

C.  F.  Boehringer  &  Sohne2  add  0.1  part  by  weight  per  litre 
of  manganese  sulphate  to  the  anode  electrolyte, — a  mixture  of 
sulphuric  and  acetic  acids, — and  obtain  smoothly  p-nitrobenzoic 
acid  at  a  lead-peroxide  anode. 

NlTROXYLENES. 

Nitro-p-xylene,  reduced  in  concentrated  sulphuric  acid, 
gives  the  corresponding  amidoxylenol  (Gattermann  and  Heider3) : 

CH3  (1) 

(2) 

(4) 
OH    (5) 

Gattermann,4  by  adding  benzaldehyde  during  the  reduction, 
obtained  the  benzylidene-derivative 

(CH3)2C6H3N  -  CHC6H5. 
\0/ 

p-Nitro-o-xylene  was  reduced  by  Elbs  and  Kopp5  in  alco- 
holic alkaline  solution  with  addition  of  sodium  acetate.  They 
obtained  good  yields  of  azoxy-,  azo-  and  hydrazoxylene. 

p-Nitro-m-xylene,  when  treated  similarly  gives  analogous 
products.6 

Elbs  and  his  pupils 6  obtained  in  the  same  manner  the 
corresponding  azoxy-,  azo-  and  hydrazo-bodies  from  o-nitro- 
benzylaniline,  p-nitrobenzylaniline,  nitrotolylaminophenylmeth- 
ane,  NH2C6H4CH2  •  C6H3CH3N02,  and  m-nitroleucomala- 
chite  green  [(CH^NCeH^CH-Ce^NOa;  but  the  last-men- 
tioned substance  was  not  reduced  to  the  azo-phase. 

1  Ztschr.  f.  Elektrochemie  8,  93  (1902). 

2D.  R.  P.  No.  117129  (1900). 

8  Ber.  d.    deutsch.  chem.  Gesellsch.  27,  1930  (1894). 

4  Ibid.  29,  3040  (1896). 

5  Ztschr.    f.  Elektrochemie  5,  110  (1898). 
8  Ibid.  7,  136  (19CO). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        173 

m-Dinitrobenzene,  on  reduction  in  concentrated  sulphuric 
acid,  is  converted  into  o-p-diamidophenol  (Gattermann  and 
Abresch  x). 

o-p-Dinitrotoluene  (2.4)  is  analogously  reduced  to  2.4.5- 
diamidocresol.  Sachs  and  Kempf2  oxidized  this  substance 
electrolytically  in  sulphuric  acid  solution  at  a  lead  anode  and 
obtained  a  medium  yield  dinitrobenzoic  acid. 

2 •  4  6-Trinitrotoluene  gives  analogously  trinitrobenzoic  acid. 

p-Dinitrostilbene.  While  carrying  out  some  experiments  on 
the  dye  "'sun  yellow/'  which  is  obtained  by  warming  p-nitro- 
toluenesulphonic  acid  with  sodium  hydroxide,  Elbs  and  Kre- 
mann3  worked  on  the  electrochemical  reduction  of  several 
stilbene  derivatives. 

They  obtained  the  following  results :  p-Dinitrostilbene,  re- 
duced in  alkaline  solution,  gives  p-azoxystilbene ;  in  hydro- 
chloric-acid solution  with  addition  of  stannous  chloride  (method 
of  C.  F.  Boehringer  &  Sohne),  p-diaminostilbene. 

o-Nitrodiphenyl  and  p-nitrodiphenyl  in  alkaline  electrolytes 
give  the  azoxy-derivatives  (Elbs);  p-nitrodiphenyl  also  gives 
inconsiderable  quantities  of  p-amidodiphenyl,  while  in  alcoholic- 
sulphuric  acid  at  platinum  and  lead  cathodes  it  is  easily  reduced 
to  p-amidodiphenyl  (Fichte  and  Sulzberger  4) . 

2.2-Dinitrodiphenyl  was  reduced  by  Wohlfahrt,5  in  accord- 
ance with  Elb's  process,  and  gave  a  very  good  yield  of  phen- 
azone,  while  in  hydrochloric-acid  electrolyte  with  the  addi- 
tion of  stannous  chloride  hydrophenazone  hydrochloride  was 
formed. 

/N0202N^ 


The  method  of  Wohlfahrt  has  been  extended  by  Ulhnann 
and  Dieterle  6  to  several  o-dinitrodiphenyl  derivatives.      The 

1  Ber.  d.   deutsch.  chem.  Gesellsch.  26,  1848  (1893). 

2  Ibid.  35,  2712  (1902). 

s  Ztschr.  f.  Elektrochemie  9,  416  (1903). 

4  Ber.  d.  deutsch.  chem.  Gesellsch.  37,  881  (1904). 

6  Journ.  f.  prakt.  Chem.  [2]  65,  295  (1902), 

8  Ber.  d.  deutsch.  chem.  Gesellsch.  37,  23  (1904). 


174        ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

corresponding    phenazones    are    formed    in    alcoholic-alkaline 
electrolytes. 

2  •  2-Dinitro-4  •  4-ditolyl  gives  the  3  •  8-dimethylphenazone, 

CH3C6H3-N 

I  II 

CH3C6H3-N, 

2  •  2-Dinitrobenzidine  gives  the  3  •  8-Diaminophenazone,  and 
Dinitrotetramethyldiaminodiphenyl  the  3  •  8-tetramethyldiamino- 
phenazone.  This  substance  is  also  produced  in  the  electric 
reduction  of  tetramethyldiaminophenazone  oxide 

(CH3)2NC6H3-N 
(CH3)2NC6H3-N 

Dinitrotetraethyldiaminodiphenyl  gives  the  3  •  8-tetraethyl 
diarninophenazone, 

Dinitroanisidine,  the  3  •  8-diaminodimethoxyphenazone 

NH2 
CH30 
CH30 

NH2 

HI.   Halogen  Derivatives  of  Mononitro-bodies. 

These  behave  quite  analogously  to  the  nitro-compounds 
containing  no  halogens.  According  to  the  process  of  Elbs,1 
if  these  substances  are  reduced  in  alcoholic-alkaline  solution, 
there  result  azoxy-,  azo-  and  hydrazo-bodies.  The  difficulties 
caused  by  the  increased  activity  of  the  nitro-group  and  the 
attackability  of  the  halogen  have  already  been  mentioned 
under  the  discussion  of  the  general  laws.  The  following  sub- 
stances have  been  investigated  in  this  manner: 

o-Chlornitrobenzene  (by-products:  o-chloraniline  and  o-ami- 
dophenol),  m-chlornitrobenzene,  p-chlornitrobenzene,  p-dichlor- 

1  Ztschr.  f.  Elektrochemie  7,  136  (1900). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        175 

(2,5) nitrobenzene  (by-products:  p-dichloraniline  and  chlor- 
aminophenol  (ClOHCeHsNH^),  o-bromnitrobenzene,  m-brom- 

52  1 

nitrobenzene,  p-bromnitrobenzene,  m-iodonitrobenzene,  p-iodoni- 
trobenzene,  o-chlor-m-nitrotoluene  (by-products:  o-chlor-m-to- 
luidine),  o-chlor-p-nitro  toluene,  p-chlor-o-nitrotoluene,  p-chlor- 
m-nitrotoluene  (by-products:  o-chlor-m-toluidine  and  o-amino- 
m-cresol) . 

Gattermann's  reaction  also  proceeds  smoothly  with  the 
halogen  derivatives,  if  the  para-position  to  the  nitro-group 
is  not  occupied. 

p-Chlornitrobenzene,  on  account  of  the  mobility  of  its  chlo- 
rine atom,  is  converted  in  concentrated  sulphuric  acid  into 
p-amidophenol  (Noyes  and  Dorrance  J). 

m-Bromnitrobenzene  gave  a  good  yield  of  bromamidophenol 
(Gattermann  and  Heider2). 

p-Brom-o-nitrotoluene  gives  the  bromamidocresol. 


XV^-LO-ij  (1) 

r  H  /NH2     (2) 
u±±2N\Br         (4-)' 
\OH       (5) 

p-Brom-m-nitrotoluene  yields  analogously  the  bromamido- 
cresol. 

/CH3  (1) 

'NH2  (3) 

,Br  (4)' 

^OR  (6) 

IV.   Nitrophenols. 

o-Nitrophenol,  reduced  electrolytically,  gives  a  good  yield 
of  o-amidophenol  both  in  alkaline-aqueous  solution  at  plati- 
num cathodes  (Lob 3)  and  in  alcoholic  potassium-hydroxide 
solution  at  lead  or  mercury  cathodes  (Elbs  4). 

o-Nitroanisol,  electrolyzed  under    the   same   conditions  as 

1  Ber.  d.   deutsch.  chem.  Gesellsch.  28,  2349  (1895). 

2  Ibid.  27,1931  (1894). 

3  Ztschr.  f.  Elektrochemie  2,  533  (1896). 

4  Journ.  f.  prakt.  Chemie.  43,  39  (1891). 


176        ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

mentioned  under  o-nitrophenol,  gives  o-azoxyanisol,  o-azoanisol, 
and  o-hydrazoanisol  (Haussermann,1  Elbs  and  Rohde2).  It 
differs,  therefore,  from  the  above  compound  in  this  respect. 
o-Nitrophenetol  behaves  similarly. 

m-Nitrophenol,  on  being  reduced,  does  not  afford  an  oppor- 
tunity for  the  quinone  formation,  and  gives,  hence,  in  alka- 
line solution  m-azophenol.  In  alcoholic-sulphuric  acid  solu- 
tion and  at  a  lead  cathode  it  is  reduced  to  m-amidophenolsul- 
phonic  acid  (Klappert 3). 

p-Nitrophenol  behaves  like  the  ortho-compound.  According 
to  Elbs,4  a  good  yield  of  p-amidophenol  is  produced  in  alkaline 
solution.  Its  ethers  p-nitroanisol  and  p-nitrophenetol  behave 
normally;  they  give  chiefly  the  azoxy-derivatives,  also  some 
p-anisidine  and  phenetidine  respectively. 

Intermediate  phases  of  the  reduction  can  be  separated  in 
the  case  of  o-  and  p-nitrophenol,  if  a  concentrated  solution  of 
aniline  hydrochloride  is  used  as  electrolyte  (Lob  5).  Compli- 
cated condensation  products  are  obtained.  It  seems  that  the 
nitrosophenols  primarily  formed  react  in  the  form  of  quinone- 
oximes  with  aniline. 

p-Nitrophenol  thus  gives  as  principal  product  dianilido- 
quinoneanil,  a  substance  which  is  also  produced  in  the  reduc- 
tion of  o-nitrophenol,  besides  a  blue  induline-like  dyestuff. 
The  mechanism  of  this  reaction  has  not  yet  been  explained. 

o-p-Dinitrophenol,  on  reduction  in  alcoholic-alkaline  solution, 
gives  a  mixture  of  amidonitrbphenol  and  diamidophenol  (Elbs  6). 
A  soluble  red  intermediate  product  is  formed  during  the  reaction. 

Trinitrophenol  (Picric  acid)  was  reduced  by  Elbs  6  in  sul- 
phuric-acid solution  to  picramic  acid 'and  diamidonitrophenol 


iChem.  Ztg.  17,209  (1893). 

2  Ztschr.  f.  Elektrochemie  7,  146  (1900). 

3  Ibid.  8,  791  (1902). 

4  Ibid.  7,  146  (1900). 
6  Ibid.  6,  441  (1900). 

8  Journ.  f.  prakt.  Chem.  [2]  43,  39  (1891). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        177 

NlTROPHENYL  ETHERS. 

Several  representatives  of  this  class  of  compounds  were 
investigated  as  to  their  behavior  in  alkaline  reduction  (Haus- 
sermann  and  Schmidt 1).  These  investigators  confirmed  the 
rules  which  Elb  established  for  nitrophenyl  ethers. 

o-Nitrophenyl  ether,  p-Nitrophenyl  ether  are  smoothly 
converted  into  azoxyphenyl  ethers. 

p-Nitrophenyl-p-tolyl  ether  gives  similarly  the  p-azoxy- 
phenyl-p-tolyl  ether. 

Hydroxyquinone-p-nitrodiphenyl  ether  yields  p-azoxydiphenyl 
ether. 

p-Aminophenyl-p-tolyl  ether  is  smoothly  formed  from  p- 
nitrophenyl-p-tolyl  ether  in  hydrochloric-acid  suspension  with  a 
tin  cathode. 

V.  Nitranilines. 

o-Nitraniline,  when  electrolyzed  in  alkaline  solution  (Elbs 
and  Rohde 2)  yields  smoothly  o-phenylenediamine,  while  the 
intermediately  recurring  nitroso-  or  hydroxylamine-phases, 
similar  to  those  in  the  p-series,  readily  rearrange  themselves 
into  quinone  derivatives. 

m-Nitraniline  behaves  differently.  This  substance,  by  elec- 
trolysis in  an  alkaline  electrolyte,  gives  a  good  yield  of  m-diam- 
inoazobenzene  (Elbs  and  Kopp,3  and  Lob  4),  also  a  little  azoxy- 
compound  and  traces  of  m-phenylenediamine.  The  reduction 
can  also  be  carried  out  to  the,  hydrazo-phase.  m-Nitraniline 
gives  o-p-dianiidophenol  in  sulphuric-acid  solution  (Gattermann)  .5 

Rohde  6  has  investigated  the  influence  of  methyl  groups  in 
the  amido-groups  in  alkaline  reduction. 

m-Nitrodimethyldniline  gives  tetramethyl-m-diamidoazo- 
benzene,  or  the  hydrazo-body.  Voight 7  reduced  it  in  con- 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  3769  (1901). 

2  Ztschr    f.  Elektrochemie  7,  144,  340  (1900). 

3  Ibid.  5,  110  (1898). 

4  Ibid.  439  (1899). 

6  Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1849  (1893). 

6  Ztschr.  f.  Elektrochemie  7,  328,  338  (1900). 

7  Ztschr.  f.  angew.  Chemie  107  (1894). 


178         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

centrated  sulphuric  acid,  and  thus  converted  it  into  1.3.4- 
dimethyl  diamidophenol. 

m-Nitrosodimethylaniline  can  be  converted  by  Gatter- 
mann's  process  into  m-p-dimethyldiamiclophenol  (Abresch  J). 

m-Nitromethylaniline  behaves  like  m-nitrodimethylaniline. 
It  is  converted  in  alkaline  electrolytes  into  dimethyl-m-diamido- 
azobenzene,  or  -hydrazobenzene.  ,'. 

p-Nitraniline,  by  reduction  in  concentrated  sulphuric  acid, 
cannot  yield  an  amidophenol  because  the  p-position  is  occupied. 
Noyes  and  Dorrance2  reduced  it  to  p-diamidobenzene.  p- 
Phenylenediamine  is  produced  in  alkaline  solution,  as  might  be 
expected  (Elbs). 

The  behavior  of  p-Aminoazobenzene  may  incidentally  be 
mentioned  here.  This  substance  by  electrolysis  in  acid  solution 
with  a  tin  cathode,  or  addition  of  stannous  chloride,  is  smoothly 
converted  into  p-phenylenediamine,3  in  the  same  manner  as 
p-nitr  aniline. 

p-Nitroacetanilide.  —  Sonneborn  4  observed  the  occurrence 
of  diacetyl-p-diamidoazoxybenzene  when  this  substance  was 
reduced  in  alkaline  solution.  This  agrees  with  the  fact  that  the 
quinone  formation  from  the  reduction  phases  of  p-nitroacet- 
anilide  is  rendered  difficult  by  the  acetyl  group.  If  on  the 
contrary,  the  electrolyte  is  kept  acid  with  acetic  acid,  the  acetyl 
derivative  of  p-phenylenediamine  and  some  phenylenediamine 
acetate  are  here  also  obtained. 

p-Nitrodimethylaniline,  in  alcoholic-alkaline  solution  and  at 
ordinary  temperature,  can  be  smoothly  reduced  to  p-amido- 
dimethylaniline  (Ronde  5)  ;  at  a  higner  temperature  a  splitting 
up  into  dimethylamine  and  p-amidophenol  occurs. 


/NH2 

C6H4<  +H20  =  C6H4<;          +  NH(CH3)2. 

XN(CH3)2  XOH 


1  Ber.  d.    deutsch.  chem.  Gesellsch.  27,  1932  (1894) 

2  Ibid.  28,  2349  (1895). 

3D.  R.  P.  No.  121835  (1900);  See  also  117007  (1900). 
*  Ztschr.  f.  Elektrochemie  6,  509  (1900). 
M.  c. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        179 

p-Nitrodiethylaniline,  by  electrolytical  reduction  in  concen- 
trated sulphuric  acid,  is  converted  into  the  important  inter- 
mediate product  of  dyestuff  manufacture,  p-amido-m-oxy- 
diethylaniline. 

/NH2 


- 

\N(C2H5)2. 

p-Nitrosodiethylaniline  1  gives  the  same  compound. 

NlTROTOLUIDINES. 

The  nitrotoluidines  when  reduced  electrolytically  in  acid 
and  alkaline  solution  behave  like  the  nitranilines.  The  position 
of  the  methyl  group  must,  of  course,  be  borne  in  mind. 

p-Nitro-o-toluidine  is  converted  by  Gattermann's  process2 
into  diamidocresol  : 

riTT       si\  /CHs     (1) 

/CHa      W 
C6H3-NH2 


\NH2     (4) 
NOH      (5). 

In  this  case  the  hydroxyl  group  occupies  the  o-position 
in  respect  to  the  original  nitro-group. 

In  alkaline  reduction  p-toluylenediamine  is  produced  (Elbs).3 

o-Nitro-p-toluidine  in  sulphuric  acid  solution  gives  the 
same  diamidocresol  as  p-nitro-o-toluidine,  the  hydroxyl  group 
occupying  the  para-position  to  the  original  nitro-group. 

The  electrical  reduction  in  an  alkaline  electrolyte  leads 
to  a  good  yield  of  o-toluylenediamine.  If  the  reduction  is 
carried  out  in  alkaline  solution,  m-nitro-p-toluidine  and  m-nitro- 
o-toluidine,  as  might  be  supposed,  are  converted  into  azoxy-, 
azo-  and  hydrazo-compounds. 

m-Nitrodimethyl-p-toluidine  gives  dimethylbenzimidazole 
(Pinnow  4) 


1  D.  R.  P.  No.  81625  (1894). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1850  (1893). 

3  Ztschr.  f.  Elektrochemie  7,  145  (1900). 

4  Journ.  f.  prakt.  Chemie  63,  352  (1901);  65,  579  (1902). 


180  .      ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

CH3 

N 


N-CH 
CH3 

and  dimethyltoluylenediamine.  The  reaction  is  carried  out 
in  Lob's  short-circuit  cell  (p.  50).  An  addition  of  graphite 
powder  accelerates  the  reaction,  which  probably  is  mainly 
caused  by  the  intermediately  occurring  nitroso-compound  split- 
ting off  water,  and  thus  yielding  the  dimethylbenzimidazole, 


/CH3 

N 


N(CH3)2 

N-CH 
CH3 

m-Nitrodimethyl-o-toluidine.  —  This     substance,    reduced   in 
alkaline  electrolytes,  gives  tetramethyl-m-diamido-p-azotoluene. 

/CH3  CH3 

H3)2(CH3)2N 
N 


andtetramethyl-m-diamido-p-hydrazotoluene. 

VI.  Nitro-derivatives  of  Diphenylamine  and  Amidotriphenylmethane. 

p-Nitrodiphenylamine,  by  /eduction  in  alcoholic-alkaline  solu- 
tion according  to  Elbs'  method,  gives  a  good  yield  of  p-amido- 
diphenylamine  (Rohde  x)  ;  the  primary  production  of  quinone 
probably  prevents  the  formation  of  the  azoxy-compound  : 

/NO,  /NHOH  .NH 

C6H4<  ->C6H4<  ^C6H4f 

\NH—  C6H5  XNH—  C6H4  XNC6H5 

/NH2 
->C6H4<( 

XNHC6H5 

Benzoyl-p-nitrodiphenylamine    cannot   yield    a    quinonedi- 


Ztschr.  f.  Elektrochemie  7,  329  (1900). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        181 

iroido-derivative.  Benzoyl-p-azoxydiphenylamine  as  well  as 
the  azo-compound  are  hence  produced  if  a  saponification  of 
the  benzoyl  group  by  the  free  alkali  is  prevented  by  neutraliz- 
ing with  acetic  acid,  or  if  ammonium  acetate  is  employed  in 
place  of  the  sodium  acetate  in  the  cathode  fluid. 

p-Nitrodiamidotriphenylmethane,  on  electrolytic  reduction 
in  concentrated  sulphuric  acid  by  a  method  of  the  Gesellschaft 
f iir  Chem.  Industrie  in  Basel x  can  be  converted  into  p-rosan- 
iline.  The  method  is  of  general  applicability:  carbinoles 
NH2-C6H4-C(OH)R2  result  in  the  reduction  of  nitro-leuco- 
bodies  of  the  type  N02-C6H4-CHR2.  (In  these  formula  R 

(4)  (1) 

denotes  aromatic  radicals  with  primary,  secondary,  or  tertiary 
amido-groups,  or  with  hydroxyl-groups.) 

Thus  is  formed  p-nitro-bitter-almond-oil-green  from  p-nitro- 
tetramethyldiamidotriphenylmethane. 

Besides  the  mentioned  products  serving  as  the  starting-point, 
there  were  also  used  p-nitrodiamido-o-ditolyl-methane,  p-nitrotetra- 
ethyldiamidotriphenyl-methane,  and  other  analogous  compounds. 

VII.  Nitroaldehydes  and  Nitroketones. 

Nitrobenzaldehyde.  —  Kaufmann  and  Hof2  subjected  m- 
nitrobenzaldehyde  to  reduction  in  alkaline-alcoholic  solution  and 
thus  obtained  m-azobenzoic  acid  as  the  principal  product  and 
m-azobenzyl  alcohol  as  a  secondary  product.  Since  the  yield 
of  the  latter  is  extremely  small  when  compared  with  that  of  the 
former,  the  authors  assumed  that  there  occurred  a  further  de- 
structive action  of  the  alkali  on  the  primarily  formed  nitrobenzyl 
alcohol  in  such  a  way  that  8  molecules  of  the  alcohol  give  1 
molecule  azoxybenzyl  alcohol  and  3  molecules  azoxybenzoic 
acid.  These  substances  are  then  converted  by  the  further 
action  of  the  current  into  the  corresponding  azo-compound, 
thus  increasing  considerably  the  quantity  ratio  of  the  primarily 
formed  acid  in  comparison  with  the  alcohol  (see  p.  188).  By 
pursuing  this  reaction  further  Lob  3  was  led  to  a  synthesis  (of 
mixed  azo-compounds;  these  will  be  mentioned  later.  If 

1  D.  R.  P.  No.  84607  (1894).  2  Chem.  Ztg.ljO,  242  (1896). 

3  Ztschr.  f.  Elektrochemie  5,  456  (1899). 


./» 


182         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

nitroaldehydes  are  reduced  in  sulphuric-acid  solution,  either 
the  free  aldehydephenylhydroxylamines,  or  their  condensation 
products  with  unchanged  nitroaldehyde,  i.e.,  nitrobenzylidene- 
aldehyde-phenylhydroxylamines,  are  formed,  m-  and  p-Nitro- 
benzaldehyde  were  investigated.  The  formation  of  these  bodies 
is  expressed  by  the  following  equations : 

JHO  /CHO 

f2H2  =  C6H4<  +H20, 

XN02  XNHOH 

xCHO 

II.  C6H4<  +OHCC6H4N02  =  H20 

XNHOH 

/CHO 
+C6H4<(    /0\ 

XN CHC6H4N02. 

On  further  reduction  the  process  can  again  repeat  itself,  so 
that  similar  higher  molecular  compounds  are  formed.  The  nitro- 
benzylidenealdehydophenylhydroxylamines  are  produced  from 
the  two  mentioned  aldehydes.  If  the  p-nitrobenzaldehyde 
is  reduced  beyond  the  compound  mentioned  in  the  equation, 
the  n-p-formylphenyl  ether  of  p-azoxybenzaldoxime  is  formed 
(Always  1),  as  shown  in  the  following  equations: 

/N02  /N02 

I.  2C6H4<f  +4H  =  CeH4\' 

\CHO  XCH  -  NC6H4CHO, 

\0/ 
/N02 
II.  2C6H4< 

XCH — NC6H4CHO + 6H 
\0/ 


/CH  —  NC6H4CHO 
C6H4< 

N\ 
I  >0  +3H20. 

/N 
C6H4        /0\ 

—  NC6H4CHO 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  3037  (1896);  36,  23  (1903);  Ztschr 
f.  Elektrochemie  3,  373  (1897). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        183 

In  the  reduction  of  aromatic  nitroketones  in  concentrated 
sulphuric  acid  the  normal  reaction,  i.e.,  the  formation  of  p- 
amidophenol  derivatives,  occurs  (Gattermann  x). 

m-Nitroacetophenone  gives  amidooxyacetophenone. 

m-Nitrobenzophenone  and  m-nitrophenyl-p-tolylketone  give 
analogous  bodies. 

In  alkaline-alcoholic  solution  Elbs  and  Wogrinz  2  obtained 
m-azoxy-  and  m-azoacetophenone  from  m-nitroacetophenone. 
The  reduction  to  the  hydrazophase  was  only  partially  successful. 

By  using  a  copper  cathode  with  addition  of  copper  sulphate, 
in  place  of  the  previously  employed  nickel  gauze  cathode,  a 
good  yield  of  m-aminoacetophenone  is  obtained  in  sulphuric- 
acid  solution;  in  alkaline  solution  a  poor  yield  results. 

m-Nitrobenzophenone,  on  electrolysis  in  alkaline  solution  at 
ordinary  temperature,  gives  an  almost  quantitative  yield  of 
m-azoxybenzophenone ;  when  reduced  at  the  boiling  tempera- 
ture, a  good  yield  of  m-azobenzophenone  is  obtained,  while 
in  sulphuric-acid  solution  m-aminobenzophenone  readily  results. 
In  the  above  processes  the  carbonyl  group  apparently  does  not 
participate  in  the  reduction  of  the  nitroketones. 

VIII.   Nitrobenzenecarboxylic  Acids. 

Nitrobenzoic  Acids. — The  m-  and  p-acids,  by  reduction  in 
alkaline  solution,  are  smoothly  and  almost  quantitatively 
converted  into  the  corresponding  azo-acids,  while  the  o-acid, 
according  to  Lob's3  researches,  under  similar  conditions  yields 
o-azoxy-  and  o-hydrazobenzoic  acid  and  complex  blue  decom- 
position products.  This  deportment  is  of  particular  interest 
because  the  o-acid  also  occupies  an  exclusive,  position  in  the 
chemical  reduction,  and  similar  experiences  seem  to  repeat 
themselves  with  the  nitrobenzenesulphonic  acids  (Gattermann  4). 

In    dilute    sulphuric    acid    Hostmann 5    converted   o-nitro- 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  3034  (1896). 

2  Ztschr.  f.  Elektrochemie  9,  428  (1903). 

3  Ibid.  2,  532  (1896). 

4  Ibid.  10,  581  (1904). 

5  Chem.  Ztg.  17,  1099  (1893). 


184         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

benzole  acid  into  o-azo-,  hydrazobenzoic  acid  and  anthranilic 
acid. 

In  concentrated  sulphuric  acid  oyxanthranilic  acid, 

/COOH  (1; 

C6H3(-NH2     (2), 

\OH       (5) 

is  produced  by  the  method  of  Gattermann,1  from  the  ortho- 
acid;  1  •  3  •  6-amidosalicylic  acid  is  formed  from  the  meta-acid. 

p-Nitrobenzoic  acid,  according  to  Clement  and  Noyes,2 
gives  the  p-amidophenolsulphonic  acid  when  electrolyzed  in 
very  concentrated  sulphuric  acid. 

The  o-  and  m-nitrobenzoic  esters,  on  electrolysis,  deport 
themselves  like  the  free  acids  (Gattermann)  .  The  latter  inves- 
tigator,3 by  preparing  the  benzylidene  compound  by  the  usual 
method,  proved  the  intermediate  formation  of  the  hydroxyl- 
amine  phase  in  the  reduction  of  the  m-acid. 

The  experiments  of  Schall  and  Klein  4  concerning  the  forma- 
tion of  nitrobenzene  from  o-nitrobenzoic  acid  are  quite  interest- 
ing. If  a  solution  of  soda  in  molten  o-nitrobenzoic  acid  (carbonic 
acid  escapes  during  the  solution  process,  so  that  a  solution 
of  the  sodium  salt  in  the  acid  itself  is  obtained)  is  electrolyzed 
at  200°  and  at  platinum  electrodes,  relatively  large  quantities 
of  nitrobenzene  are  produced;  at  the  same  time  a  gas  is  evolved 
at  the  anode  (C02?).  During  an  electrolysis  lasting  one  to 
two  hours,  with  0.8  to  1  amp.,  about  1  cc.  was  obtained.  The 
experiments  were  made  with  the  expectation  of  finding  a 
reaction  among  the  aromatic  acids  similar  to  Kolbe's.  Although 
in  the  case  of  the  aliphatic  acids  a  limit  hydrocarbon  is  formed 
by  the  union  of  two  anions  with  splitting  off  of  carbonic 
acid,  for  instance, 

2CH3COO  =  C2 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1850  (1893);    27,  1932  (1894). 

2  Am.  Chem.  Journ.  16,  511  (1894). 

8  Ber.  d.  deutsch.  chem.  Gesellsch.  29,  3040  (1896). 
4  Ztschr.  f.  Elektrochemie  5,  256  (1898). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        185 
an  analogously  formed  product,  o-dinitrodiphenyl, 

2N02C6H4COO  =  N02C6H4  -  C6H4N02  +  2C02, 

could  not  be  obtained  from  o-nitrobenzoic  acid. 

The  following  nitrobenzene  carboxylic  acids  (or  their  esters^ 
on  reduction  in  concentrated  sulphuric  acid,  react  in  a  normal 
manner : 

m-Nitro-p-toluic  Acid.1 — Amidocresotinic  acid  is  formed: 

COOH  (1) 
(3) 
W 
XOH       (6) 

The  methyl  and  ethyl  esters  behave  analogously. 
Nitrocumic  Methyl  and  Ethyl  Esters  give  the  corresponding 
amidophenol  esters : 

/coon  (i) 

~r  -tl2     H^6-H-2\\ 
V\ 

XOH        (6) 

NlTROCINNAMIC    AdDS, 

Orthonitrocinnamic  Acid.  —  This  substance,  by  reduction  in 
concentrated  sulphuric  acid,  is  converted  into  the  sulphate 
of  amidooxycinnamic  acid  which,  on  being  heated  in  hydrochloric 
acid,  is  in  turn  converted  into  oxycarbostyril.  The  methyl 
ester,1  under  like  conditions,  behaves  similarly. 

m-Nitrocmnamic  Acid. — This  acid,  treated  analogously, 
gives  amidocoumarin,  which  is  produced  from  the  m-amido- 
oxycinnamic  acid  by  a  splitting  off  of  water : 

/CH  =  CHCOOH  /^V 

NH2C6H4<  -H20  -»  NH2C6H4< 

XOH  \c 

1Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1851  (1893);    27,  1935  (1894). 


186         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  ethyl  ester  leads  to  the  same  coumarin — either  by 
saponification  of  the  nitre-ester  before  the  reduction,  or  by 
the  splitting  off  of  alcohol  from  the  intermediately  formed 
amidooxycinnamic  ester. 

NlTROPHTHALIC   ACIDS- 

a-Nitrophthalic  Acid  was  converted  by  Elbs' 1  method  into 
azo-  and  and  hydrazophthalic  acid;  traces  of  a-aminophthalic 
acid  were  also  produced. 

/?-Nitrophthalic  Acid  behaves  similarly. 

Nitroisophthalic  Acid. — This  substance,  by  electrolytic  re- 
duction in  concentrated  sulphuric  acid,  according  to  Gatter- 
mann,2  is  converted  into  the  sulphate  of  oxyamidoisophthalic 
acid.  Nitroterephthalic  acid  gives  an  amidooxyterephthalic  acid. 

NlTROBENZONITRILES. 

m-Nitrobenzonitrile  can  be  converted  by  Elbs'  3  method, 
depending  upon  the  conditions  of  the  experiment,  either  without 
saponification  into  m-azobenzonitrile,  or  with  saponification  into 
m-azoxybenzamide  and  m-azobenzamide. 

p-Nitrobenzonitrile  gives  analogously  azo-  and  azoxynitrile 
or  azo-  and  azoxybenzamide. 

IX.     Nitrobenzenesulphonic  Acids. 

Those  sulphonic  acids  which  have  the  SOsH-group  in  the 
m-position  to  the  nitro-group,  have  been  particularly  inves- 
tigated. Under  the  conditions  chosen  by  Elbs,4  they  yield 
universally  azo-  and  hydrazo-bodies.  Thus  nitrobenzene-m- 
sulphonic  acid,  o-nitrotoluene-p-sulphonic  acid,  p-nitrotoluene-o- 
sulphonic  acid  are  converted  into  the  corresponding  azo-  or 
hydrazo-compounds. 

p-Nitrobenzenesulphonic  Acid  also  behaves  normally  on 
electrolytic  reduction  in  slightly  alkaline  solution  at  nickel 
cathodes  (Elbs  and  Wohlfahrt  5) ;  it  yields  azo-,  or  hydrazo- 

1  Ztschr.  f.  Elektrochemie  7,  143  (1900). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1852  (1893). 

3  Ztschr.  f.  Elektrochemie  7,  143  (1900). 

4  Ibid.  7,  142  (1900). 
6  Ibid.  8,  789  (1902) 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        187 

acid.  In  the  case  of  the  o-nitro-acid,  on  the  contrary,  the 
reduction  is  far  from  normal;  complicated  products  and  o- 
aminosulphonic  acid  are  chiefly  produced. 

p-Nitrotoluenesulphonic  Acid. — The  Gesellschaft  f.  Chem. 
Industrie  of  Basel l  prepares  orange  dyes  by  using  as  cathode 
fluid  an  alkaline  solution  of  the  yellow  condensation  products 
of  p-nitrotoluenesulphonic  acid, 

/N02 
CH3-C6H3< 

\S03H 

(e.g.  a  mixture  of  azoxystilbenedisulphonic  acid,  azostilbene- 
disulphonic  acid,  and  dinitrostilbenedisulphonic  acid).  The 
reduction,  however,  must  not  be  continued  until  amido-com- 
pounds  result. 

Elbs  and  Kremann  2  have  likewise  investigated  the  electro- 
chemical behavior  of  the  dye  "'sun  yellow"  formed  in  alkaline 
solution  of  the  p-nitrotoluenesulphonic  acid,  and  found  the 
following : 

1.  "Sun  yellow"   consists  chiefly  of   p-azoxystilbenedisul- 
phonic  acid. 

2.  Reduced  in  alkaline  solution  it  yield;  as  end  product, 
p-azotoluenedisulphonic  acid. 

3.  In  acid  solution  with  addition  of  stannous  chloride  there 
are    formed    p-diaminostilbenedisulph'onic    acid    and    p-tolui- 
dinesulphonic  acid. 

The  following  may  be  remarked  concerning  the  reduction  in 
acid  solution:  According  to  Haussermann,3  metanilic  acid  is: 
smoothly  obtained  from  m-nitrobenzenesulphonic  acid  in  dilute 
sulphuric  acid;  in  concentrated  acid  3.4-amidophenolsulphonic 
acid  results  (Gattermann4). 

o-Nitrotoluene-p-sulphonic  Acid  gives  similarly  2  -4  •  5-amino- 
cresolsulphonic  acid. 

1  Eng.  Pat.  No.  22482  (1895). 

2  Ztschr.  f.  Elektrochemie  9,  416  (1903).   ' 

3  Chem.  Ztg.  17,  209  (1893). 

4  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  1938  (1894). 


188         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

p-Dinitrostilbenedisulphonic  Acid  (according  to  Elbs  and 
Kremann1),  like  p-azostilbenesulphonic  acid,  yields  in  alkaline 
solution  p-azotoluenedisulphonic  acid,  while  in  acid  solution 
with  the  addition  of  stannous  chloride  the  end-product  is  p- 
diaminodibenzyldisulphonic  acid. 

p-Dinitrodibenzyldisulphonic  Acid  yields  in  alkaline  solution 
p-azodibenzyldisulphonic  acid;  hi  acid  solution,  in  the  presence 
of  stannous  chloride,  p-diaminodibenzyldisul phonic  acid. 

X.  Other  Reductions  of  Nitro-compounds. 

Lob  2  has  utilized  the  possibility  of  conducting  the  reduction 
in  alkaline  solution  up  to  the  azo-phase  for  accomplishing  a 
direct  electrosynthesis  of  mixed  azo-bodies  and  azo-dyes. 

The  components  of  the  desired  compounds  are  reduced  in 
equimolecular  proportions  under  conditions  which  make  possible 
the  union  of  the  two  radicals  during  the  azo-phase.  By  means 
of  this  method  azo-compounds  in  which  the  substitutents  are 
in  any  desirable  position  to  the  azo-bond,  and  which  are  not 
obtainable  by  the  Griess  method,  can  be  prepared. 

Thus  m-nitrobenzaldehyde,  which  in  alkaline  solution 
gives  equal  molecules  of  m-nitrobenzoic  acid  and  m-nitrobenzyl 
alcohol,  yields  as  chief  product  m-m-azobenzoic-acid-benzyl- 
alcohol, 

m-COOHC6H4N  =  NC6H4CH2OH, 

and  as  secondary  product s-m-azobenzoic  acid  and  m-azobenzyl 
alcohol. 

Kaufmann  and  Hof 3  (p.  181)  had  subjected  m-nitrobenz- 
aldehyde to  reduction  in  alkaline  solution,  but  they  did  not 
observe  the  occurrence  of  the  mixed  azo-compound;  they  found 
only  the  azo-alcohol  and  the  azo-acid,  and  explained  the  poor 
yield  of  the  former  by  the  behavior  of  the  m-nitrobenzyl  alcohol 
towards  alkalies,  as  shown  in  the  equation : 


*1.  c. 

3  Ber.  d.  deutsch.  chem  Gesellsch.  31,  2201  (1898);  Ztschr.  f.  Elektrochemie 
.5,  456  (1899). 

3  Chem.  Ztg.  20,  242  (1896). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        189 
/N02 


8  C6H4< 

\CH2OH 


'N\ — 7N\ 

C6H4<  \0/         \C6H4 

lOOHHOOCX 


4/         \0/  \C6H4+6H20. 

\CH2OH 


Of  the  other  bodies  prepared  by  Lob  according  to  the 
principle  mentioned,  the  following  may  be  noted: 
Azo-p-toluene-m-benzoic  acid, 

p-CH3C6H4N  =  NC6H4COOH-m, 

is  prepared  from  p-nitrotoluene  and  m-nitrobenzoic  acid. 
m-m-Sulphoazobenzoic  acid, 

m-S03HC6H4N  =  NC6H4COOH-m, 

is  obtained  from  nitrobenzenesulphonic  acid  and  nitrobenzoic 
acid  in  a  pure  state  and  in  the  form  of  the  acid  potassium  salt. 
The  latter,  which  can  be  crystallized  from  alcohol,  can  be 
obtained  by  neutralizing  the  electrolyte  with  hydrochloric 
acid  and  concentrating  the  solution.1 

o-Methylazobenzene  is  formed  from  o-nitrotoluene  and  nitro- 
benzene as  a  red  oil  boiling  at  185°-188°  at  28  m.m.  pressure. 

The  mixed  azo-compounds  are  always  formed  in  company 
with  the  azo-derivatives  of  the  components,  so  that  their 
yields  are  often  not  very  favorable. 

Elbs  and  Keiper2  have  found  that  o-nitroazo-compounds 
are  smoothly  converted  into  phentriazoles  by  electrochemical 
reduction  in  slightly  alkaline  solution. 

/\N  =  NC6H4OH 

+  4H  =  2H20  + 
'N02 


u 


NC6H4OH. 


1  Recent  experiments  by  van  Emster,  Bonn  (1904). 

2  Journ.  f.  prakt.  Chemie  67,  580  (1903). 


190         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

There  result  from 

o-Nitrobenzeneazophenol,  phenolphentriazole  ;  from 

o-Nitrobenzeneazosalicylic  acid,  salicylic-acid-phentriazole, 

.OH  M 

N  =  NC6H3<  OH 

XCOOH^I  NC6H3< 

N02  \/\N/  COOH; 

and  from 

o-Nitrobenzeneazo-a-naphthol,  a-naphtholphentriazole  : 

,N 

NCioH6OH. 


XI.  Nitro-Derivatives  of  the  Naphthalene,  Anthracene,  and 
Phenanthrene  Series. 

Since  only  the  nitro-group  is  subject  to  reduction  by  the 
cathodic  action  of  the  current  on  nitro-compounds,  nothing 
new  can  here  be  added  regarding  the  possible  reduction  phases. 
The  conditions  which  with  the  benzene  derivatives  lead  to 
certain  stages,  cannot  always  be  directly  applied  to  these  sub- 
stances; this  is  due  to  the  influence  which  the  whole  molecule 
possesses  over  the  reaction  velocity  of  the  separate  processes. 
This  deportment  is  especially  shown  by  the  nitro-derivatives  of 
the  anthracene  series.  Nevertheless,  some  of  the  more  general 
conditions  also  obtain  here;  for  instance,  nitronaphthalene 
derivatives  in  acid  electrolytes  at  attackable  cathodes,  accord- 
ing to  the  process  of  Boehririger  &  Sohne,1  are  also  easily 
reduced  to  amines.  Gattermann's  method  has  also  been  ser- 
viceable in  the  preparation  of  amidonaphthols. 

a:  -Nitronaphthalene,2  in  aqueous  acetone  solution  was  re- 
duced by  Voigt  to  nitrosostyrol  besides  a  little  naphthylamine. 
The  latter  is  quantitatively  obtained  if  a-nitronaphthalene  is 

*D.  R.  P.  No.  116942  (1899);  117007  (1900) 
2  Ztschr.  f.  angew.  Chemie  (1894)  108. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        191 

reduced  in  a  hydrochloric-acid  electrolyte  with  an  attackable 
cathode,  or  with  addition  of  salts  of  the  latter.1 

ai-Nitronaphthalene-as-sulphonic  acid  was  converted  by 
Voigt 2  into  hydrazonaphthalenesulphonic  acid  and  some 
naphthylamine.  Gattermann3  obtained  by  his  method  the 
aminonaphtholsulphonic  acid  in  a  normal  manner.  Analogously 
behave 

«i-Nitronaphthalene-/?3-  and  /?4-sulphonic  acids  and  the  di- 
sulphonic  acids  (/?2,  /?s,  and  firf*)  of  a-Nitronaphthalene.4 

(a:  10:4)  Dinitronaphthalene  (according  to  a  patent  of  the 
Badische  Anilin-  u.  Sodafabrik)  alone,  or  mixed  with  (0:10:2) 
dinitronaphthalene,  gives  in  concentrated  sulphuric-acid  solu- 
tion a  product  which,  by  heating  with  dilute  acids,  can  readily 
be  converted  into  naphthazarin,5 

0:10:3-  and  0:10:4-  Dinitronaphthalene,  if  reduced  according 
to  Tafel,  in  a  mixture  of  acetic  and  sulphuric  acid  with  prepared 
lead  cathodes,  gives  the  1-5-  and  1  •  8-naphthylenediamines 
(Holler  6). 

/N02 

o:-Nitro-/?-naphthyl  ethyl  ether,  Ci0H6\  . — This  naph- 

X)C2H5 

thol  ether,  unlike  the  nitrophenol  ethers,  gives  a-amido-/?-naph- 
thyl  ethyl  ether  as  end-product  of  the  alkaline  reduction 
(Rhode7). 

o-Nitroanthraquinone  has  been  reduced  by  Holier 8  in 
alcoholic-sulphuric  acid  and  in  slightly  alkaline  solution  to  o- 
amidoanthraquinone.  By  electrical  oxidation  in  concentrated 
sulphuric  acid  there  is  formed,  according  to  Weizmann,9  nitro- 
oxyanthraquinone;  with  alternating  currents  alizarinamide  was 
produced;  and  in  the  presence  of  glycerin,  mannit,  etc.,  blue  and 

1  D.  R.  P.  No.  116942  (1899);  117007  (1900) 

2  Ztschr.  f.  angew.  Chemie.  1894,  108. 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  26,  1852  (1893). 
4D.  R.  P.  No.  81621  (1893). 

5D.  R.  P.  No.  79406  (1894). 

8  Elektrochem.  Ztschr.  10,  199,  222  (1903-1904). 

7  Ztschr.  f.  Elektrochemie  7,  340  (1900). 

8  Ibid.,  741,  797  (1901). 

8  Fr.  P.  No.  265292  (1897). 


192         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

green  reduction  products  resulted.     The  action  of  the  cathodic 
current  on 

1  •  2-Dinitroanthraquinone   and  i  •  5-Dinitroanthraquinone  in 
a  solution  of  glacial  acetic  acid  with  addition  of  sulphuric  acid 
produces  diamidoanthraquinones; 1  the  yield,  however,  is  poor. 
The  employment  of  lead  cathodes,  as  shown  by  Tafel,  may 
perhaps  increase  the  latter. 

According  to  experiments  of  the  Badische  Anilin-  u.  Soda- 
fabrik,2  a  dinitroanthraquinone  dissolved  in  fuming  sulphuric 
acid  is  changed  by  electrolytic  reduction  to  blue  mordant  dyes. 

Dinitroanthrarufindisulphonic  Acid  and  Dinitrochrysazindi- 
sulphonic  Acid. — These  substances  are  easily  reduced  electrolyti- 
cally  in  sulphuric-acid  solution  to  diamidoanthrarufindisul- 
phonic  acid  and  diamidochrysazindisulphonic  acid.3 

9-Nitrophenanthrene  has  been  converted  by  Schmidt  and 
Strobel 4  into  9-azoxyphenanthrene  by  Elbs'  process. 

2-Nitrophenanthrenequinone  in  acid  solution  at  lead  cathodes 
gives  2-aminophenanthrenequinone  (Moller). 

2  •  7-Dinitrophenanthrenequinone  is  converted  in  acid  solution 
into  2  •  7-diamidophenanthrenequinone  (Moller). 

XII.  Nitroso-  and  Nitro-Derivatives  of  the  Pyridine  and  Quinoluie 

Ser  es. 

Nitrosopiperidine,  on  electrolytic  reduction  in  sulphuric- 
acid  solution  (Ahrens  5),  gives  piperylhydrazine,  piperidine,  and 
ammonia;  at  the  anode  there  are  formed  at  the  same  time  a 
diamine,  CioHig^,  of  the  fatty  acid  series,  and  two  isomeric 
amido valeric  acids,  besides  hydrochloric  acid  and  piperidine. 
Under  similar  conditions 

Nitroso-a-pipecoline  gives  a-methylpiperylhydrazine,  a- 
pipecoline  and  ammonia  at  the  cathode,  and  at  the  anode  a 

1  Elektrochem.  Ztschr.  10,  199,  222  (1903-1904). 

2  D.  R.  P.  No.  92800,  92998  (1896). 
3D.  R.  P.  No.  105501  (1898). 

4  Ber.  d.  deutsch.  chem.  Gesellech.  36,  2512  (1903). 

5  Ztschr.    f .    Elektrochemie  2,   578    (1896) ;     Ber.  d.  deutsch.  Gesellsch. 
30,  f33  (1897);  31,  2272  (1898). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        193 

diamine  and  an  amidocaproic  acid.      In  the  same  manner  the 
other    nitroso-derivatives  of  homologous  piperidines  on    elec- 
trical reduction  give  corresponding  piperylhydrazines. 
Ahrens  and  Sollmann l  similarly  prepared  from 
Nitroso-3-pipecoline  the  /?-pipecolylhydrazine ;   from 
Nitroso-^-pipecoline  the  7"-pipecolylhydrazine ;  from 
Nitroso-a-a-lupetidine     the    a-a-dimethylpiperylhydrazine ; 
from 

Nitrosoaldehydecopellidine  the  aldehydecopellidinehydra- 
zine;  and  from 

Nitroso-s-trimethylpiperidine  the  s-trimethylpiperylhydra- 
zine. 

Nitrosotetrahydroquinoline.  —  Concerning  tne  experiments 
of  Ahrens  and  Widera  2  on  the  oxidation  of  nitroso-derivatives 
of  pyridine  and  quinoline  there  is  yet  to  be  mentioned  the 
smooth  conversion  of  nitrosotetrahydroquinoline  into  tetrahy- 
droquinoline.  The  nitroso-group  is  found  as  nitric  acid  in 
the  anode  fluid. 

4-Nitroquinoline  and  i-o-Nitroquinoline,  reduced  in  con- 
centrated sulphuric  acid,  give  1.4-oxyamidoquinoline  and 
1.4-amidooxy quinoline  (Gattermann  3). 

4-Mtro-3-toluquinoline  gives  likewise  a  4-amido-l-oxy- 
3-toluquinoline  • 

N02  r  NH2  r 

HsC  A/N/?  ^-CHaf^^Y^ 

rt  I       AA^ 

^ 


N  OH  N 


3.  AMINO-DERIVATIVES. 

Aniline.  —  Rotondi  4  electrolyzed  aniline  in  an  ammoniacal 
solution.  After  a  period  of  three  days,  during  which  hydrogen 
was  continually  evolved  at  the  negative  pole  and  a  tarry  sub- 

1  Chem.  Ztschr.  2,  414  (1903). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  31,  2276  (1898). 

3  Ibid.  27,  1939  (1894). 

4  Jahresh.  f.  Chemie,  1884,  270. 


194         ELECTROCHEMISTRY  OF  ORGANIC   COMPOUNDS. 

stance  was  deposited  at  the  positive  pole,  Rotondi  interrupted 
the  electrolysis  and  was  able,  with  more  or  less  certainty,  to 
establish  the  following  processes  : 

1.  The  formation  of  diazo-compounds  : 

C6H5NH2(HN03)  +  HN02  -  C6H5N2N03  +  2H20. 

2.  The  formation  of  diazoamido-compounds  : 

2C6H5NH2  +  HN02  =  CeHsNaNHCeHg  +  2H20. 
C6H5N2N03  +  C6H5NH2  =  C6H5N2NH  •  C6H5  +  HN03. 

3.  The  formation  of  azo-compounds  by  direct  oxidation  of 
aniline  : 

2C6H5NH2  +  20  =  2H2 


4.  The  formation  of  amidoazo-compounds  by  molecular 
rearrangement  of  diazoamido-compounds.  The  nitrous  acid 
and  nitric  acid  were  oxidation  products  of  the  ammonia  which 
was  added. 

C.  F.  Boehringer  &  Sohne  add  a  manganese  salt  to  the 
electrolyte  1  in  the  presence  of  a  strongly  dissociating  acid  and 
thus  smoothly  oxidize  aniline  to  quinone. 

The  fact  that  aromatic  amines  are  often  directly  convertible 
by  oxidation  into  dyes,  early  directed  attention  to  the  elec- 
trolytic oxidation  of  amines  for  the  direct  preparation  of  dyes. 
The  investigations  of  Goppelsroder,2  which  were  carried  out 
some  time  ago,  have  primarily  this  end  in  view. 

Goppelsroder  has  compiled  the  technical  results  in  a  small 
pamphlet:  "  Farbelektrochemische  Mitteilungen  "  (Miihlhausen, 
1889).  They  may  be  briefly  mentioned  here. 

If  a  galvanic  current  is  conducted  through  acid  or  neutral 
aqueous  solutions  of  aniline,  there  is  formed  at  the  positive 

1  D.  R.  P.  No.  117129  (1900). 

2Dringler,  Polytechn.  Journ.  221,  75;  223,  317,  634;  234,  92,  209  (1876)- 
1877).  Cf.  also:  Concerning  the  Preparation  of  Dyes,  and  their  Simul- 
taneous Formation  and  Fixation  in  the  Fibers  with  the  Aid  of  Electrolysis, 
Goppelsroder,  Reichenberg,  1885. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        195 


pole,  besides  other  coloring  matters,  aniline  black, 
Under  similar  conditions  dyes  are  obtained  at  the  positive  pole 
from  the  salts  of  toluidine,  methylaniline,  diphenylamine,  di- 
tolylamine,  and  phenyltolylamine. 

On  electrolysis  of  a  mixture  of  anthraquinone  and  caustic 
potash  Goppelsroder  obtained  alizarine. 

The  numerous  experiments  which  led  to  the  formation  of 
dyes  at  the  anode,  when  aniline,  toluidine,  methylaniline, 
diphenylamine,  methyldiphenylamine  and  naphthylamine  or  their 
salts  were  electrolyzed,  have,  however,  not  been  scientifically 
investigated  and,  hence,  still  remain  unsolved.  The  same* 
holds  true  of  Goppelsroder's  investigations  concerning  the  oxi- 
dation of  phenol  and  anthraquinone.  The  most  important  dis- 
covery is  the  fact  that  aniline  salts  smoothly  yield  aniline  black 
at  the  anode;  the  naphthylamine  salts  give  naphthylamine- 
violet.1 

Voigt,2  by  the  electrolytic  oxidation  of  suitable  mixtures 
of  bases,  prepared  rosaniline,  chrysaniline,  safranine,  and  p- 
leucaniline.  His  object  in  these  researches  was  the  same  as 
that  of  Goppelsroder;  namely,  the  preparation  directly  in  the 
bath  of  the  important  dyes  of  the  aniline  series. 

1  The  following  literary  data  will  serve  as  a  guide  : 
Research  1.*  Preparation  of  aniline  black. 

Research  2.f  Electrolysis  of  aniline  with  excess  of  aniline. 

Electrolysis  of  toluidine. 

Electrolysis  of  mixtures  of  aniline  with  toluidine  isomers. 
Research  3.{  Electrolysis  of  aniline  and  toluidine  salts  in  the  presence 
of  potassium  nitrate,  nitrite,  or  chlorate  in  aqueous  solution. 
Research  4.§  Electrolysis  of  tne  salts  of  methylaniline. 

Electrolysis  of  the  salts  of  diphenylamine. 

Electrolysis  of  the  salts  of  methyldiphenylamine. 

Electrolysis  of  phenol. 

Electrolysis  of  the  salts  of  naphthylamine. 

Research  5.  |[  Conversion  of  anthraquinone  into  alizarine  by  the  elec- 
trolysis of  a  mixture  of  anthraquinone  and  potassium  hydroxide. 

2  Ztsch.  f.  angew.  Chemie,  1894,  p.  107. 

*  Dingier,  Polytechm.  Journ.  221,  75  (1676). 
•\Ibid.  223,  317  (1877). 
%  Ibid.  223,  634  (1877). 
§  Ibid.  224,  92  (1877). 
||  Ibid.  224,  209  (1877). 


196         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

If  electrolytic  oxygen  is  permitted  to  act  upon  aniline  in 
concentrated  acetic-acid  solution,  acetanilide  is  formed  (Voigt) ; 
by  using  a  dilute  solution,  however,  amidohydroquinone  is 
obtained. 

These  investigations  have  not  been  satisfactorily  concluded, 
which  is  also  the  case  with  those  of  Foelsing,1  who,  by  the 
oxidation  of  p-phenylenediamine  and  benzene-p-phenylene- 
diamine,  obtained  indigo-blue  dyes. 

According  to  Lob's 2  experiments  (see  p.  176)  by  electro- 
lytic reduction  of  nitro-compounds  in  a  solution  of  fuming 
hydrochloric  acid  in  an  excess  of  an  aromatic  amine,  induline-like 
dyes — not  identical  with  the  known  induline  dyes — are  obtained. 
Szarvasy,3  however,  by  anodic  electrolysis  of  molten  aniline 
hydrochloride,  obtained  electrolytically  the  indulines  themselves. 
If  a  mixture  of  aniline  and  aniline  hydrochloride  is  electrolyzed 
at  70°-90°,  there  is  obtained  a  rich  yield  of  azophenine,  the 
known  intermediate  product  of  the  indulines.  By  electrolysis 
of  the  pure  molten  salt  at  about  150°-300°,  induline,  anilidoindu- 
line,  and  induline  6  B,  besides  the  intermediate  products  of  the 
induline  formation,  could  be  detected  as  products  of  the  anodic 
oxidation.  The  oxidizing  agent  in  these  processes,  which  were 
carried  out  without  an  oxygen-containing  electrolyte,  was 
chlorine,  which  probably  first  produces  azo-compounds  that 
react  further  in  the  molten  mass  with  aniline  hydrochloride. 

The  interesting  research  of  Votocek,  Zenisek  4  and  Sebor  5 
may  also,  be  referred  to  in  this  connection.  This  permits  the 
Sandmeyer-Gattermann  reaction  (substitution  of  the  diazo-group 
by  chlorine  and  bromine)  to  be  carried  out  electrolytically.  For 
this  purpose  the  diazotized  solution  of  the  amine  is  electrolyzed 
— for  instance  50  g.  aniline,  120  g.  HC1,  38.5  g.  NaN02 — between 
copper  electrodes  with  addition  of  cuprous  chloride  or  copper 
sulphate.  At  the  end  of  the  experiment  (ceasing  of  the  nitrogen 

1  Ztschr.  f.  Elektrochemie  2,  30  (1895). 

2  Ibid.  6,  441  (1900). 

3  Ibid.  6,403(1900). 

4  Ibid.  5,  485  (1899). 
6  Ibid.  7,  877  (1901). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        197 

evolution)  64%  chlorbenzene  and  10%  azobenzene  could  be 
isolated.  This  process  could  be  used  successfully  for  obtaining 
brombenzene  by  addition  of  copper  sulphate  and  potassium 
bromide,  also  for  p-chlortoluene  and  /?-chlor naphthalene.  The 
method  is  not  applicable  for  preparing  fluorbenzene  and 
a-chl  or  naphthalene. 

The  direct  diazotization  and  preparation  of  azo-dyes  in  one 
electrochemical  process  was  discovered  by  Lob.1  His  method — 
an  anodic  process — is  based  on  the  following  principle : 

As  is  well  known,  azo-dyes  are  generally  prepared  by  diazo- 
tizing  the  amine  in  acid  solution  or  suspension  at  a  low  tempera- 
ture and  then  bringing  together  the  diazotized  solution  with  the 
usually  alkaline  solution  of  the  components  to  be  joined. 

The  same  effect  can  be  reached  electrochemically,  if  amine, 
nitrite,  and  the  coupling  components  of  the  compound  desired  are 
simultaneously  exposed  in  a  neutral  or  sometimes  alkaline 
electrolyte  to  the  anodic  action  of  the  current  at  an  unattackable 
electrode. 

The  first  stage  of  the  process  consists  undoubtedly  in  the 
action  of  the  discharged  N02  ions  on  the  amine,  as  shown  in  the 
equation 

RNH2  +  N02  ->  RN  =  NOH  +  OH. 

However,  if  an  amine  alone  is  subjected  to  the  anodic  current 
action  in  the  presence  of  the  nitrite,  complicated  products 
result ;  besides  the  action  of  the  N02  ions  upon  the  amido-group 
and  the  typical  decomposition  of  the  diazo-body  by  the  electro- 
lyte, substitution  and  oxidation  processes  seem  to  occur. 

It  is  therefore  necessary  to  add  components  to  the  electrolyte 
already  before  the  electrolysis,  which  react  so  rapidly  with  the 
intermediately  occurring  diazo-bodies  that  the  latter  is  with- 
drawn from  the  other  disturbing  influences. 

Phenols  are  particularly  suited  as  addition  substances  for 
fixing  the  diazo-bodies.  Experiments  have  shown  that  the 
coupling  of  the  diazo-compound  with  the  acid  component  takes 

i  Ztschr.  f.  Elektrocheinie  10,  237  (1904). 


198         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

place  much  more  rapidly  than  its  decomposition  by  the  men- 
tioned influences.  In  the  presence  of  phenols  the  formation  of 
the  azo-dyes  can  therefore  be  made  the  predominating  one.  It 
is  very  evident  that  in  this  process  amines  are  not  applicable  as 
components  for  coupling  purposes,  because  they  are  themselves 
subject  to  the  action  of  the  nitrite  ions,  and  other  complicated 
reactions. 

The  experiments  are  generally  conducted  by  putting  the 
aqueous  solution,  or  suspension,  of  amine,  coupling  component- 
prefer  ably  in  the  form  of  a  soluble  salt — and  nitrite,  in  equi- 
molecular  proportions,  in  the  anode  chamber,  which  is  suitably 
separated  from  the  cathode  chamber  by  a  diaphragm.  Platinum 
is  the  best  anode  material;  any  suitable  metal  can  serve  as 
cathode.  The  current  conditions  chosen  may  vary  greatly — from 
50-600  amp.  per  square  meter  of  anode  surface.  It  is  very 
important  that  the  anode  fluid  be  stirred  during  the  whole 
experiment. 

An  increase  in  temperature  is  sometimes  beneficial,  but  is 
generally  unfavorable  for  the  yield  and  purity  of  the  dyes. 
An  artificial  lowering  of  the  temperature,  which  is  necessary 
for  the  chemical  diazotizing  process,  is  never  required.  Several 
examples  are  classified  in  the  following  table : 


Benzidine 

Sodium 

Anode 
solutions: 

Sodium 
Sulphanilate 

/?-Naphthol 
Sodium 

NaphthioH- 
ate 

Sodium 
Nitrite 

Dianisidine 
/?-Naphthol 
Sodium 

"Mit  rifp 

Benzidine 

Sodium 
Salicylate 

Sodium 

1.4-Naphthyl- 
aminesul- 
phonate. 

/?-Naphthol 

Nitrite 

,,. 

Nitrite 

Sodium 

Water 

Sodium 

Water 

Water 

Nitrite 

Hydroxide 

Water 

Results  : 

Orange  II 

Congo 

Dianisidine- 

Chrvsamine 

Rocceline 

blue 

G 

Dimethylaniline,  electrolyzed  in  sulphuric-acid  solution  at 
platinum  electrodes  in  the  presence  of  some  chromic  acid,  gives 
tetramethylbenzidine.  In  this  case  the  oxidizer  is  chromic 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        199 

acid;    the  current  action  consists  only  in  the  continual  re- 
generation of  the  latter  (Lob1). 

Triamidotriphenylmethane. — The  Farbwerken  vorm.  Meister, 
Lucius,  &  Briming,2  by  electrolytically  oxidizing  those  sub- 
stances which  are  formed  in  the  treatment  of  the  hydro- 
chloric-acid salts  of  homologues  of  triamidotriphenylmethane 
with  fuming  sulphuric  acid  in  the  presence  or  absence  of  sul- 
phur, succeeded  in  preparing  blue,  basic  triphenylmethane 
dyes. 

4.  PHENOLS. 

Phenol. — Bunge,3  Bartoli  and  Papasoli  4  submitted  phenol 
to  the  action  of  the  electric  current.  Bunge  observed  that  the 
decomposition  of  potassium  phenolate  was  analogous  to  that 
of  an  acid  or  a  salt;  the  potassium  phenolate  was  split  up  into 
K  (cation)  and  CeHsO  (anion),  the  latter  combining  with 
water  to  form  phenol,  with  the  liberation  of  oxygen.  Bartoli 
and  Papasogli,  on  electrolyzing  solutions  of  phenol  in  potas- 
sium and  sodium  hydroxide,  and  using  electrodes  of  coke, 
graphite,  and  platinum,  obtained  an  acid  having  the  com- 
position C7H604,  which  melted  at  93°,  reduced  ammoniacal 
silver  solution  and  Fehling's  solution  on  being  heated,  and 
when  in  aqueous  solution  was  not  precipitated  by  acids.  When, 
however,  retort  coke  was  used  as  the  positive  electrode,  an 
extensive  decomposition  of  the  phenol  occurred  and  a  resin 
was  formed. 

On  subjecting  a  neutral  potassium  phenolate  solution  to  the 
action  of  the  electric  current  they  were  able  to  isolate  a  com- 
pound, C65H48022,  soluble  in  alkali  and  precipitated  from  such 
solutions  by  mineral  acids.  This  latter  compound  on  being 
oxidized  with  nitric  acid  formed  picric  acid.  When  allowed 
to  remain  in  solution  in  the  presence  of  dilute  acids  for  a  pro- 


1  Ztschr.  f.  Elektrochemie  7,  603  (1901). 

2D.  R.  P.  No.  100556  (1897). 

8  Ber.  d.  deutsch.  chem.  Gesellsch.  3,  296  (1870). 

4  Gazz.  chim.  14,  103  (1884). 


200         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

longed  period,  it  underwent  decomposition  according  to  the 
following  equation: 

C65H48022  +  H20  -  C44H30Oi  5  +  C2iH2008. 

The  electrolysis  of  neutral  sodium-phenolate  solution  gave 
an  acid  having  the  formula  C29H2oOs,  which  likewise  is  decom- 
posed on  boiling  with  dilute  acids: 


The  compound  Ci2Hi003  is  soluble  in  alcohol,  melts  at  75°, 
and  is  isomeric  with  the  hydroquinone  ether  obtained  by 
Etard  from  chlorchromic  acid  and  phenol.  It  has  tne  com- 
position 

OHHO 


The  relations  which  exist  between  the  potential  and  the 
pressure  with  which  a  discharged  ion,  like  chlorine,  bromine, 
or  iodine  reacts  with  phenol  nave  been  determined  by  Zehr- 
lant  1  with  the  following  results  : 

The  substitution  of  chlorine  in  phenol  in  dilute  acid  solution 
does  not  take  place,  nor  does  that  of  bromine,  since  the  oxida- 
tion begins  earlier,  at  a  lower  potential,  than  the  halogen 
discharge.  Iodine  also  does  not  act  on  phenol  in  acid  solution. 
A  bromination  can,  however,  be  obtained  if,  on  the  one  hand, 
the  potential  for  the  beginning  of  the  oxidation  is  raised  by 
decreasing  the  oxygen-  or  hydroxyl-ionic  concentration;  on 
trie  other  hand,  the  discharge  potential  of  bromine  is  lowered 
by  increasing  the  bromine  concentration,  i.e.,  if  concentrated 
hydrobromic  acid  (multiple  normal)  is  employed,  bromination 
occurs. 

Thymol.  —  In  alkaline  solution  halogen  substitution  takes 
place  very  rapidly  with  phenols.  This  fact  has  led  to  the 

lZtschr.  f.  Elektrochemie  7,  501  (1901). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        201 

electrolytic  preparation  of  dithymoldiiodide,  the  antiseptic 
aristol,  as  made  by  Messinger  and  Vortmann 1  by  the  electrolysis 
of  an  alkaline  solution  of  thymol  with  the  addition  of  potassium 
iodide. 

Directions  for  the  preparation  of  a  whole  series  of  iodides  of 
phenols  are  mentioned  in  the  same  patent  papers;  e.g.,  from 
p-naphthol,  phenol,  resorcin,  salicylic  acid,  cresotinic  acid,  carva- 
crol,  p-isobutylphenol,  o-m-p-isobutylcresol,  etc. 

Nosophen,  a  tetraiodophenolphthalein,  from  phenolphtha- 
lein  (Classen  and  Lob  2),  is  obtained  in  like  manner. 

With  these  methods  of  preparation  there  corresponds  a  simi- 
lar process,  which  the  Societe  chimique  des  usines  du  Rhone  anc. 
Gilliard,  Monnet  et  Cartier  patented  in  Germany,3  for  the  elec- 
trolytic preparation  of  eosine  and  other  halogen  derivatives  of  the 
fluorescein  group.  The  solutions  of  the  fluorescems  in  alkali- 
hydroxide  or  in  alkali- carbonate  solution  serve  as  anode  fluids. 
The  halogens,  such  as  chlorine  or  bromine,  are  introduced  into 
the  anode  compartment,  whereby  salts  of  the  halogen  acids 
form  and  simultaneous  halogenation  of  the  fluorescems  occurs. 

Since  the  salts  are  again  decomposed  by  the  current,  with 
splitting  off  of  the  halogen,  which  in  turn  reacts  on  the  fluores- 
ceins,  the  quantitative — very  important  for  bromine  and  iodine 
— utilization  of  the  halogen  can  take  place.  The  well-known 
eosins  are  said  to  be  obtained  in  excellent  yields  and  in  a  high 
state  of  purity. 

Phenylmercaptan. — Bunge,4  who  had  obtained  ethyldi- 
sulphide  from  ethyl  mercaptan  (see  p.  65),  also  investigated 
phenylmercaptan.  Phenyldisulphide,  (C6H5)2S2,  was  formed 
from  phenylmercaptan  at  the  positive  pole. 

Hydroquinone. — If  an  acid  hydroquinone  solution  with 
addition  of  a  manganese  salt,  according  to  the  process  of  C.  F. 
Boehringer  &  Sohne,5  ,is  electrolyzed,  quinone  is  smoothly  pro- 

1  D.  R.  P.  No.  64405  (1891). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  28,  1603  (1895). 

3  D.  R.  P.  No.  108838  (1899). 

*  Ber  d.  deutsch.  chem.  Gesellsch.  3,  911  (1870). 
5  D.  R.  P.  No.  117129  (1900). 


202         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

duced.  But  if  a  weak  sulphuric-acid  solution  without  addition 
is  electrolyzed,  quinonehydrone  is  precipitated  at  the  anode 
(Liebmann *) . 

Resorcin. — Alefeld  and  Vaubel,2  by  electrolytic  oxidation, 
have  obtained  dyes  of  different  shades  from  resorcin  and  other 
hydroxyl  derivatives  of  the  aromatic  series,  such  as  gallic  acid, 
tannic  acid,  fkioresceins  and  eosins.  An  investigation  of  the 
dyes  was  not  made. 

Pyrogallol  (pyrogallic  acid). — According  to  A.  G.  Perkin 
and  F.  M.  Perkin,3  purpurogallin  CnHgOs,  can  readily  be  ob- 
tained by  electrochemical  oxidation  of  pyrogallol  in  dilute 
sulphuric  acid  with  addition  of  sodium  sulphate  at  a  platinum- 
iridium  anode. 

Gallic  Acid  behaves  likewise.  Purpurogallincarboxylic 
acid,  CiiH705COOH,  is  probably  obtained. 

Eugenol. — The  firm  v.  Heyden  Nchfg.4  obtains  vanillin  elec- 
trolytically  from  eugenol. ,  The  latter  is  rearranged  by  alkalies 
into  isoeugenol  and  then  oxidized  electrolytically  in  alkaline 
solution: 

/OH  /OH 

C6H3f-OCH3  ->  C6H3(-OCH3 

\CH2CH  =  CH2  \CH  =  CHCH3 

Eugenol  Isoeugenol 

/OH  /OH 

C6H3f-OCH3          +3  0  -» C6H3f-OCH3  +CH3COOH. 
\CH=CHCH3  \CHO 

Isoeugenol  Vanillin 


5.  ALCOHOLS,  ALDEHYDES,  KETONES,  AND  QUINONES. 

These  classes  of  bodies,  owing  to  their  peculiarity  in  being 
both  reducible  and  oxidizable,  present  many  interesting  phe- 
nomena respecting  their  electrolytic  behavior.  Since  every 


1  Ztschr.  f.  Elektrochemie  2,  497  (1896). 
2Chem.  Ztg.  22,297  (1898). 
»  Proceed.  Chem.  Soc.  19,  58  (1903). 
4  D.  R.  P.  No.  92007  (1895). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        203 

electrolytic  cell  performs  both  functions  at  both  electrodes,  the 
problem  presents  itself  to  apply  t>oth  of  these  effects  of  the 
current  to  one  and  the  same  substance.  We  shall  see  that  this 
possibility  has  actually  been  realized  in  individual  cases. 

Salicin,  saligenin-glucose,  by  the  action  of  the  enzymes 
ptyalin  and  emulsion,  is  known  to  split  up  into  glucose  and 
saligenin  (i.e.  o-oxybenzyl,  e.g.  salicyl  alcohol).  On  boiling  with 
dilute  acids  the  same  decomposition  occurs,  but  saligenin  is  res- 
mined  to  saliretin.  Tichanowitz  1  and  Hostmann  2  found  that 
salicin  on  electrolysis  splits  up  into  glucose  and  salicyl  alcohol, 
the  latter  being  partially  oxidized  to  salicylic  aldehyde  and 
salicylic  acid. 

Benzaldehyde. — Kauffmann,3  by  electrolyzing  benzaldehyde 
in  a  12-15%  solution  of  potassium  bisulphite,  obtained  at 
the  cathode  a  mixture  of  hydrobenzom  and  isohydrobenzi'on. 
According  to*  his  statements,4  an  alcoholic  solution  of  sodium 
hydroxide  is  more  suitable  for  the  reaction  than  the  aqueous 
solution  of  bisulphite.  Other  aldehydes  and  ke tones  show  a 
behavior  similar  to  that  of  benzaldehyde,  as  will  be  explained 
under  the  individual  substances. 

Tafel  and  Pfeffermann  5  have  discovered  a  useful  method 
for  preparing  amines.  They  electrolytically  reduce  oximes 
and  phenylhydrazones  in  sulphuric-acid  solution.  Thus 

Benzylidenephenylhydrazone,  the  condensation  product  of 
benzaldehyde  and  phenylhydrazine,  gives  43  per  cent,  of  the 
theoretical  yield  of  benzylamine,  besides  some  aniline: 

C6H5CH  =NNHC6H5 +4H  ->  C6H5CH2NH2  +C6H5NH2. 

Benzaldoxime,  by  reduction,  is  split  up,  yielding  69  per  cent, 
of  the  theoretically  possible  quantity  of  benzylamine: 

C6H5CH  =  NOH + 4H  ->  C6H5CH2NH2  +  H20. 


1  Chem.  Centralb.  613  (1861). 
2Chem.  Ztg.  17,  1099  (1893). 

3  Ztschr.    f.  Elektrochemie  2,  365  (1895) 

4  Ibid.  4,  461  (1898). 

6  Ber.  d.  deutsch.  chem.  Gesellsch.  35,  1510  (1902). 


204         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Salicylaldehydephenylhydrazone,  by  electrolytical  oxidation 
in  alkaline  solution  at  a  platinum  anode  can  be  converted  into 
salicyl-a-osazont:  (Biltz  l). 

20HC6H4CH  =  NNHC6H5  +  0 
OHC6H4C—  CC6H4OH 

II     II  +H20. 

C5H5HNN   NNHC6H5 

Acetophenone,  CeHs-CO-CHs.  —  Acetophenone  yields  aceto- 
phenonepinacone, 


5\  /C 

>C(OH)-C(OH)< 
X  XCH3 


if  reduced  in  alcoholic  sodium  hydroxide  (Kauffmann2).  Elbs 
and  Brand3  employed  an  alcoholic-alkaline  solution  and  lead 
cathodes;  electrolyzing  at  the  boiling  temperature,  they  also 
obtained  acetophenonepinacone  and  a  moderate  yield  of  me  thy]  - 
phenyl  carbinol: 

C6H5CH(OH)CH3. 

In  sulphuric-acid  solution  and  at  lead  cathodes  the  same  sub- 
stances are  produced  in  almost  equal  yields. 

Acetophenoneoxime,  investigated  by  Tafel  and  Pfeffer- 
mann4  in  the  same  way  as  benzaldoxime,  gives  phenylethyl- 
amine  sulphate  : 

5\  CeH5\ 

C  =NOH+4H  -4  CHNH2  +H20. 


/ 


Benzophenone,  on  being  reduced  in  alkaline  solution  at  lead 
cathodes  (Elbs  and  Brand5),  gives  benzhydrol  almost  quanti- 
tatively, 


1  Lieb.  Am.  305,  167  (1899). 

2  Ztschr.  f.  Elektrochemie  4,  461  (1898). 

3  Ibid.  8,  784  (1902). 
41.  c. 

5  I.e. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        205 

\ 
>CHOH, 


while  in  sulphuric-acid  solution  the  reduction  becomes  more 
complicated.  If  the  warm  solution  is  electrolyzed  with  a  mod- 
erate current  density,  there  occurs  as  chief  product  /?-benz- 
pinacoline,  which  is  to  be  regarded  as  a  molecular  rearrange- 
ment product  of  the  primarily  formed  benzophenonepinacone 
with  splitting  off  of  water: 


x 
(OH)—  C(OH)  -»  C6H5-CCOC6H5  +H20. 


With  a  very  small  current  density  and  at  a  low  temperature 
(0°-2°)  the  yield  of  /?-benzpinacoline  is  trifling,  benzhydrol  and 
diphenyl  me  thane  being  chiefly  produced. 

If  the  alcohol  and  sulphuric  acid  are  replaced  by  acetone 
and  phosphoric  acid  respectively,  and  the  electrolysis  is  carried 
out  with  a  high  current  density  and  with  a  warm  solution, 
there  will  be  formed,  by  the  action  of  phosphoric  acid  with 
simultaneous  splitting  off  of  water,  a-benzpinacoline,  the  re- 
arrangement product  of  benzophenonepinacone: 


0\ 
C(OH)—  C(OH)  -»  0—  \C< 

C6H5      CeHs/  XC6H5. 


Benzophenoneoxime.  —  This  substance,  on  electrolysis  in  a 
60%  sulphuric  acid  at  lead  and  mercury  electrodes  —  the  latter  be- 
ing preferred  on  account  of  the  difficultly  soluble  sulphate  which 
is  formed  —  is  reduced  to  benzhydrylamine  (Tafel  and  Pfeffer- 
mann  l  : 


v  esv 

>C  =  NOH  +  4H  ->  >CHNH2  +  H20. 

/  C6H5/ 

Elbs  and  Brand2  also  investigated  the  following  ketones: 
M.  c.  21.  c. 


206         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Phenyl-p-tolylketone,  by    alkaline  reduction,   gives  almost 
quantitatively  phenyl-p-tolylcarbinol  : 


The  same  product,  together  with  phenyl-p-tolylpinacone, 
is  produced  in  sulphuric-acid  solution  at  a  low  current  density 
and  temperature.  With  a  higher  current  density  and  tempera- 
ture the  formation  of  carbinol  is  trifling,  and  a  good  yield  of 
phenyltolylpinacone  is  obtained  : 


Phenyl-m-xylylketone.  —  The  reaction  product  of  the  alka- 
line reduction  is  a  liquid  modification  of  phenyl-m-xylylcarbinol; 
but  in  sulphuric-acid-acetone  solution  at  the  boiling  temperature 
phenyl-m-xylylpinacone  is  obtained.  The  yield  of  the  latter  is 
40-50  per  cent,  of  that  theoretically  possible. 

Phenyl-a-naphthy  Ike  tone.  —  A  satisfactory  yield  of  phenyl- 
a-naphthylcarbinol  is  obtained  in  alkaline  electrolytes;  in  acid 
solution  only  phenyl-a-naphthyl-/?-pinacoline, 


5 


results.  This  is  due  to  the  fact  that  phenylnaphthylpinacone  is 
very  sensitive  towards  acids;  thus  only  its  conversion  product  is 
obtained  above. 

The  same  is  true  in  acid  solution  of 

p-Ethoxybenzophenone,  which  yields  p-ethoxybenz-/?-pina- 
coline  : 


C2H5OC6H 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        207 

p-Oxybenzophenone.  —  While  this  ketone  is  not  reducible  in 
alkaline  electrolytes,  the  normal  reduction  product,  p-oxybenz- 
pinacone,  is  produced  in  alcoholic  -sulphuric  acid: 

C6H5C(H)C6H4OH 


p-Oxybenzophenonebenzoate.  —  This  substance  is  reduced  to 
the  carbinol  in  sodium-acetate  solution.  To  prevent  saponifica- 
tion  during  reduction,  the  free  alkali  must  be  continually  neu- 
tralized with  acetic  acid. 

Phthalyl-p-aminobenzophenone.  —  This  compound,  by  reduc- 
tion in  sulphuric-acid  solution,  gives  a  poor  yield  of  pinacone. 

Elbs  and  Brand  sum  up  the  results  of  their  investigation  as 
follows  : 

1.  The   electrochemical   reduction   of   ketones   in    alkaline 
solution  at  lead  cathodes  gives  the  same  products  as  the  chemical 
reduction  with  sodium  amalgam  or  with  zinc  dust  and  alkali; 
the  process  is  in  many  cases  suitable  for  the  preparation  of 
benzhydrols. 

2.  The  electrochemical  reduction  of  ketones  in  acid  solution 
(dilute  sulphuric  or  phosphoric  acid)  at  lead  cathodes  leads  to 
pinacones;  if  these  are  sensitive  towards  acids,  the  corresponding 
a  or  ft  pinacolines  are  obtained  in  their  stead.     For  this  reason 
the  electrochemical  process  is  not  so  generally  applicable  for  the 
preparation  of  aromatic  pinacones  as  the  method  employing 
glacial  acetic  acid  and  zinc  dust,  which  has  been  worked  out  by 
Elbs  and  Schmidt;1  but  the  electrochemical  reduction  is  more 
energetic  than  that  with  zinc  dust  and  glacial   acetic   acid. 
Fatty  ketones  are  reduced  like  the  aromatic  ketones,  with  the 
difference  that  fatty  and   fatty-aromatic  ketones   give  simul- 
taneously alcohols  and  pinacones,  whereas  pure  aromatic  ketones 
yield  chiefly  only  pinacones. 

Tetramethyldiamidobenzophenone,  Michler's  ketone,  accord- 
ing to  Kauffmann,2  when  electrolytically  reduced  in  alcoholic 

1  Journ.  f.  prakt.  Chem.  51,  591  (1895). 

2  Ztschr.  f.  Elektrochemie  4,  461  (1898). 


208         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 
sodium-hydroxide  solution,  gives  the  corresponding  benzhydrol: 


/C6H4N(CH3)2 

C0<  +2H  =  CHOH  ; 

\C6H4N(CH3)2  \C6H4N(CH3)2 

Elbs  and  Brand  l  obtained  the  same  result. 

Escherich  and  Moest  2  made  an  extensive  investigation  with 
the  object  of  preparing  electrolytically  tetra-alkylated  diamido- 
benzhydrols.  They  discovered  that,  by  observing  certain 
experimental  conditions,  the  reduction  can  at  will  be-directed  to 
the  hydrol  or  the  pinacone.  This  is  particularly  true  with 
Michler's  ketone.  We  can  thus  obtain  chiefly  pinacone,  for 
instance,  by  employing  copper  cathodes  in  a  dilute  sulphuric- 
acid  solution;  nickel  cathodes,  under  the  same  conditions,  yield 
about  equal  quantities  of  pinacone  and  hydrol,  wnile  by  using 
lead  cathodes  and  mercury  cathodes,  hydrol  is  chiefly  produced. 
Moreover,  the  pinacone  reaction  occurs  the  more  easily  the  more 
concentrated  the  solution  is  of  the  acid.  Because  of  the  resisti- 
bility  of  the  resulting  reduction  products  towards  anodic  oxygen, 
separate  electrode  chambers  are  not  required. 

Since 

Tetramethyldiamidodiphenylmethane, 

(CH3)2NC6H4 


(CH3)2NC6H 

on  electrolytic  oxidation  m  dilute  sulphuric  acid  at  a  lead 
anode  also  readily  yields  the  hydrol,  the  oxidizing  action  of  the 
current  can  also  be  employed,  besides  the  reducing  action, 
in  the  preparation  of  the  hydrol,  if  a  mixture  of  tetra- 
methyldiamidodiphenylmethane  and  tetramethyldiamidobenzo- 
phenone  in  molecular  proportion  is  electrolyzed.  Escherich 
and  Moest  actually  obtained  a  very  good  yield  of  the  hydrol, 
—  without  an  evolution  of  gas,  —  at  the  cathode  and  anode. 
Dibenzylketone.  —  Elbs  and  Brand3  have  published  a  short 

1  Ztschr.  f.  Elektrochemie  8,  786  (1902). 

2  Ibid.  8,  849  (1902);  D.  R.  P.  No.  133896  (1901). 

3  Ztschr.   f.  Elektrochemie  8,  784  (1902). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        209 

note  on  this  substance.  The  reduction  seems  to  take  place 
like  that  of  other  ke tones;  but  the  nature  of  the  oily  reaction- 
product  was  not  determined. 

Benzile. — The  aromatic  diketone  benzile,  CeHsCO  •  CO  •  C&H.5, 
gives  peculiar  results  (Kauffmann l) .  By  reduction  in  an  alka- 
line alcoholic  solution  a  whole  series  of  bodies  is  formed,  i.e., 
benzoic  acid,  benzilic  acid,  tetraphenylery thrite : 

C6H5-CHOH 
C6H5-COH 

C28H2604  = 

C6H5-COH 
C6H5-CHOH, 

and  a  substance,  C28H2603,  containing  one  less  atom  of  oxygen, 
which  has  probably  the  constitution 

C6H5-CHOH 
C6H5-COH 

C6H5-CH 

I 
C6H5-CHOH. 

Tetraphenylerythrite  is  also  formed  by  the  direct  reduction  of 
benzom. 

Benzoin. — Benzile,  by  reduction  in  dilute  alcoholic  sodium 
hydroxide  and  in  alcoholic  sulphuric  acid,  according  to  James,2 
can  inversely  be  converted  into  benzoin.  Oxidation  of  benzoin 
in  alkaline  and  sulphuric-acid  solution  gives  a  poor  yield  of  ben- 
zoic acid.  In  alcoholic  hydrochloric  acid,  especially  at  a  high 
current  density,  benzile  is  formed. 

Anthraquinone. — The  first  researches  concerning  the  elec- 
trolysis of  this  substance  were  made  by  Goppelsroder  (see  p. 
194) ,  who,  by  suspending  anthraquinine  in  potassium  hydroxide, 


1  Ztschr.  f.  Elektrochemie  4,  461  (1898). 

2  Journ.  Am.  Chem.  Soc.  21,  889  (1899). 


210         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

suspected  reduction  products,  such  as  oxyanthranol  or  hydro- 
anthroquinone,  among  the  substances  deposited  on  the  cathode 
electrode.  If  the  current  is  sent  through  a  mixture  of  anthra- 
quinone  and  molten  alkali,  oxyanthraquinone  first,  then  alizarate, 
and  then  purpurate,  is  supposed  to  be  formed.  These  experiments, 
however,  require  to  be  repeated  with  greater  exactitude. 

According  to  Weizmann,1  anthraquinone,  dissolved  in  concen- 
trated sulphuric  acid,  is  converted  by  electrolytic  oxidation 
into  monoxy-,  dioxy-,  and  trioxyanthraquinone.  An  addition 
of  oxalic  acid  to  the  sulphuric  acid  is  suitable  for  obtaining 
dioxy  anthraquinone.  A  nitrooxy  anthraquinone,  which  is  con- 
vertible by  electrical  reduction  into  amidoalizarin,  is  similarly 
obtained  from  mononitroanthraquinone.2  The  amidoalizarin  can 
be  directly  obtained  from  nitroanthraquinone  if  its  solution  is 
electrolyzed  with  an  alternating  current.  The  sulphonic-acid 
derivatives  of  anthraquinone  behave  like  anthraquinone. 

The  phenomena  occurring  with  these  oxidations  were  later 
more  accurately  investigated  by  Perlin.3  From  anthraquinone 
in  92%  sulphuric  acid  90  to  96%  dioxy  an  thraquin  ones  and  a 
small  quantity  of  monoanthraquinones  were  obtained.  Besides 
a-  and  /?-monooxyanthraquinone,  quinizarin,  alizarin,  and  pur- 
purin  could  be  isolated.  If  the  anthraquinone-sulphuric  acid 
solution  is  employed  as  cathode  fluid,  anthranols,  anthrones, 
and  hydroanthranols  are  formed.  If  the  sulphuric-acid  con- 
centration of  the  anode  solution  is  increased,  there  are  formed 
sulphurated  oxyanthraquinories. 

a-Monwitroanihraquinone,  under  like  conditions,  gives  a 
nitrooxyanthraquinone  besides  a  mixture  of  di-  and  trioxyan- 
thraquinone. 

Dibromanthraquinone  gives  violet  crystals,  perhaps  a  tetni- 
oxydibromanthraquinone. 

Phenanthrenequinone,  according  to  Perlin,  is  electrolytically 
oxidized  in  concentrated  sulphuric-acid  solution  to  a  mixture 
of  mono-  and  trioxyphenanthrenequinone. 

1  F.  P.  No.  265291  (1897). 

2  F.  P.  No.  265292  (1897). 
»Diss.  Berlin,  March,  1899. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        211 

All  these  oxidation  processes  illustrate  the  possibility  already 
mentioned  (p.  132)  of  introducing  oxygen  electrolytically  into 
the  benzene  nucleus. 

6.  ACIDS. 

The  electrolysis  of  aromatic  acids  by  no  means  offers  results 
which  are  comparable  to  those  obtained  by  the  electrolysis 
of  aliphatic  acids.  In  so  far  as  the  aromatic  acids,  or.  their 
salts,  act  as  electrolytes,  a  regeneration  of  the  acid  from  the 
anion  RCOO  and  water  v  with  evolution  of  oxygen,  occurs 
almost  exclusively.  A  splitting  off  of  carbonic  acid,  which 
makes  possible  the  manifold  reactions  of  aliphatic  acids,  almost 
never  occurs  here.  The  results  obtained  with  aromatic  acids 
are,  therefore,  only  of  a  more  general  interest  so  far  as  the 
acids,  by  substitutions  in  the  benzene  nucleus,  can  act  as 
cathodic  or  anodic  depolarizers,  and  can  in  this  way  exert 
reduction  and  oxidation  effects. 

Benzoic  Acid. — Benzoic  acid  and  its  salts  were  examined 
by  several  investigators,  first  by  Matteuci,1  then  by  Brester,2 
but  most  thoroughly  by  Bourgoin.3 

The  result  of  all  these  investigations  is  to  show  that  here 
no  secondary  reactions  take  place,  as  was  observed  in  the  case 
of  the  fatty  acids,  but  that  the  only  effect  of  the  current  is  to 
produce  a  separation  into  hydrogen  (or  metal)  and  the  acid 
radical,  the  latter  regenerating  the  acid  at  the  positive  pole. 

In  an  alkaline  solution  it  is  possible  to  so  increase  the  oxida- 
tion that  the  benzoic  acid  is  destroyed.  The  decomposition  prod- 
ucts which  then  appear  at  the  anode  are  carbon  dioxide,  carbon 
monoxide,  and  sometimes  acetylene.  The  odor  of  bitter 
almonds  is  also  frequently  observed. 

A  thorough  investigation  was  made  by  Lob,4  who  employed 
a  current  having  a  potential  of  6-7  volts  and  a  current  density 
of  15-20  amp.  per  sq.  cm.  and  obtained  a  small  quantity  of 

1  Bull.  soc.  chim.  10,  209  (1868). 

2  Jahresb.  f.  Chem.  (1866),  87. 

3  Bull.  soc.  chim.  9,  431  (1867). 

4  Ztschr.  f.  Elektrochemie,  2,  663;  3,  3  (1896). 


212         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

a  substance  containing  sodium,  but  the  chemical  nature  of 
which  has  not  yet  been  determined.  There  is  formed  besides 
this  compound  a  small  quantity  of  benzaldehyde,  as  well  as 
acetylene  and  carbon  monoxide.  Under  no  circumstances  do 
diphenyl  or  other  hydrocarbons  occur;  nor  do  fatty  acids 
appear,  which  is  otherwise  generally  the  case  in  an  extensive 
oxidation  of  this  character. 

According  to  the  investigations  of  Schall,1  diphenyl  does, 
however,  occur  if  a  solution  of  sodium  benzoate  in  molten 
benzoic  acid  is  electrolyzed  at  100  volts  between  silver  elec- 
trodes. 

Benzoic  Esters. — Tafel  and  Friedrichs,2  by  conducting  the 
electrolysis  in  alcoholic-aqueous  sulpnuric  acid  at  lead  or  mer- 
cury cathodes,  obtained  methyl  benzyl  ether  and  the  ethyl  benzyl 
ether  from  benzoic  methyl  and  benzoic  ethyl  esters  respectively. 
Mettler,3  by  a  similar  arrangement,  obtained  chiefly  benzyl  alco- 
hol and  some  benzyl  methyl  ether  from  benzoic  methyl  ester. 

The  esters  of  monochlor-  and  brombenzow  acids  also  yield  the 
corresponding  ethers  and  alcohols. 

Thiobenzoic  Acid. — On  electrolyzing  this  acid  Bunge 4  ob- 
tained the  bisulphide  of  benzoyl. 

Sulphobenzoic  Acid. — This  acid,  according  to  the  statements 
of  the  same  investigator,  is  not  changed  by  the  current. 

Phthalic  Acid. — Bourgoin  5  states  that  the  electrolysis  of 
this  acid  and  of  its  neutral  or  alkaline  salts  resulted  in  the 
formation  of  the  unchanged  acid  at  the  positive  pole.  The 
appearance  of  small  quantities  of  carbon  dioxide  and  carbon 
monoxide,  however,  was  an  evidence  that  a  small  portion  of  the 
acid  had  undergone  oxidation. 

The  potassium  salt  of  the  mono-ethyl  ester  of  phthalic  acid, 
when  electrolyzed  by  Brown  and  Walker,6  became  dark-colored, 
and  a  resinous  substance  was  formed,  but  the  isolation  of  any 

1  Ztschr.  f.  Elektrochemie  <>,  102  (1899). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  37,  3182  (1904). 

3  Ibid.  37,  3692  (1904). 

4  Ibid.  3,  296  (1870). 

6  Jahresb.  f.  Chem.  631  (1871). 
8  Lieb.  Ann.  274,  67  (1893). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        213 

new  electrolytic  product  was  not  possible.  Phthalic  esters, 
according  to  Tafel  and  Friedrichs,1  can  be  readily  reduced  in 
the  presence  of  sulphuric  acid  at  lead  or  mercury  cathodes. 

Phenylacetic  Acid. — This  acid,  electrolyzed  in  the  form  of 
its  potassium  salt  by  Slawik,2  yielded  free  phenylacetic  acid. 

p-Toluic  Acid. — According  to  an  incomplete  research  by 
Labhardt  and  Zschoche,3  p-toluic  acid  in  alkaline  solution  at 
polished  platinum  anodes  is  oxidized  to  terephthalic  acid : 

CH3  .COOH 

— >  C&H.4\ 
X)OH  XCOOH. 

p-Toluenesulphonic  Acid. — This  acid  gives  at  platinum  and 
lead  electrodes  a  poor  yield  of  p-sulphobenzoic  acid  (Sebor  4). 

Cinnamic  Acid. — Cinnamic  acid,  investigated  by  Brester,5 
showed  a  similar  behavior  in  the  electrolysis  of  both  the  free  acid 
and  the  neutral  solutions  of  its  salts.  Lob  6  has  reported  an 
accidental  observation  on  the  formation  of  bromstyrene  by 
electrolysis  of  cinnamic  acid  in  the  presence  of  potassium  bromide. 

In  acid  solution  Marie7  converted  cinnamic  acid  almost 
quantitatively  into  hydrocinnamic  acid. 

Benzylmalonic  Acid. — When  this  acid  in  the  form  of  its 
ethyl-potassium  salt  was  submitted  to  electrolysis  by  Brown  and 
Walker  8  it  exhibited  a  behavior  materially  different  from  that  of 
malonic  acid.  The  solution  became  dark-colored,  but  contained 
no  new  compound.  If  oxidation  occurred,  it  was  a  complete 
oxidation  into  carbon  dioxide  and  carbon  monoxide,  such  as  has 
been  observed  in  the  case  of  unsaturated  acids. 

However,  when  v.  Miller  9  electrolyzed  the  ethyl-potassium 

U.  c. 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  7,  1051  (1874). 

8  Ztschr.  f.  Elektrochemie  8,  93  (1902). 

4  Ibid.  9,  370  (1903). 

5  Jahresb.  f.  Chem.  87  (1866). 

8  Ztschr.  f.  Elektrochemie  3,  46  (1896). 
7  Compt.  rend.  136,  1331  (1903). 
8Lieb.  Ann.  274,67  (1893). 

9  Ztschr.  f.  Elektrochemie  4,  57  (1897). 


214        ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

salt  of  this  acid  in  the  presence  of  potassium  acetate,  not  only 
a-methylhydrocinnamic  ester, 

/COOCsHg 
C6H5CH2CH< 

XCH3 

but  also  dibenzylsuccinic  ester, 

C6H5  -  CH2  -  CH  -  COOC2H5 
C6H5  -  CH2  -  CH  -  COOC2H5, 

was  produced,  as  was  to  be  expected  according  to  the  Brown- 
Walker  reaction.  There  are  also  present  the  normal  by- 
products of  the  electrolysis  of  such  kind  of  acids,  in  this  case 
hydrocinnamic  acid  and  cinnamic  acid.  On  repeating  these 
experiments,  Hauser  1  was  also  able  to  isolate  propylbenzene,  the 
formation  of  which  was  brought  about  by  the  electrolysis  of 
hydrocinnamic  ester — readily  formed  from  the  material  started 
with — and  potassium  acetate. 

The  electrolysis  of  the  ester-salt  of  benzylmalonic  acid 
with  potassium  butyrate  and  caproate  takes  place  just  as  with 
potassium  acetate.  Good  yields  of  propylhydrocinnamic  ester 
and  amylhydrocinnamic  ester,  besides  dibenzylsuccinic  ester 
and  cinnamic  and  hydrocinnamic  esters,  are  obtained. 

Dibenzylacetic  Acid.  —  This  substance,  on  electrolysis  of 
its  potassium  salt,  and  a  mixture  of  this  salt  with  fatty  acid  salts, 
gives  no  tangible  products. 

Salicylic  Acid. — The  formation  of  yellow  mordant  dyes, 
which  are  obtained  by  the  electrolytic  oxidation  of  aromatic 
oxycarboxylic  acids  in  sulphuric-acid  Solution  (Badische  Anilin- 
u.  Sodafabrik2),  seems  to  be  based  on  the  frequently  mentioned 
introduction  of  oxygen  into  the  benzene  nucleus.  The  materials 
serving  as  starting-point,  aside  from  salicylic  acid,  were  sym- 
metrical m-dioxybenzoic  acid,  gallic  acid,  tannin,  gallaminic  acid, 
esters  of  the  acids,  m-  and  p-oxybenzoic  acid,  and  other  oxy-acids. 

1  Dissertation  Munich  (1901). 
2D.  R.  P.  No.  85390  (1895). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        215 

The  electrolytic  introduction  of  halogens  into  salicylic  acid 
lias  been  mentioned  under  phenols  (p.  201). 

Von  Miller  and  Hofer  l  have  applied  their  method  for  the 
electrolysis  of  organic  oxy-acids  to  several  aromatic  acids  con- 
taining substituents;  these  experiments  may  briefly  be  men- 
tioned here. 

Phenyl-/?-lactic  Acid.  —  This  acid  gives  at  the  anode 
benzaldehyde,  besides  resinous  bodies. 

Mandelic  Acid.  —  This  substance  yielded  at  the  anode  chiefly 
carbonic  acid,  a  little  carbon  monoxide,  and  also  benzaldehyde. 
The  same  body  was  formed  in  the  electrolysis  of  phenyl- 
glyceric  acid. 

Sulphoanthranilic  Acid.  —  This  substance,  according  to  a 
patent  2  of  Kalle  &  Co.,  can  be  converted  into  anthranilic  acid 
if  electrolyzed  in  neutral  or  slightly  acid  solution  at  a  mercury 
cathode. 

7.  ACID  AMIDES  AND  NITRILES. 

According  to  the  investigations  of  Baillie  and  Tafel,3  the 
reduction  of  acid  amides  in  sulphuric-acid  solution  at  lead 
cathodes  leads  to  amines,  as  shown  in  the  equation: 

RCONH2  +  4H  =  RCH2  •  NH2  +  H20. 

Benzamide  yields  only  a  little  benzylamine;  benzaldhyde, 
which  probably  contained  benzyl  alcohol,  was  also  formed. 
In  a  similar  manner 

Dimethylbenzamide  gives  dimethylbenzylamine; 

Acetanilide  gives  ethylaniline  ; 

Acetyl-o-rtoluidine  gives  ethyl-o-toluidine  ;   and 

Succinanil  gives  phenylpyrrolidone  : 

CH2—  COv  CH2—  C(X 

I  >NC6H5+4HH  NC6H5+H20. 

CH2—  CCK  CH2 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  27,  461  (1894). 

2D.  R.  P.  No.  146716  (1902). 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  32,  63  (1899). 


216         .ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

(The  same  reaction  in  the  aliphatic  series,  p.  119,  in  the 
pyridine  and  quinoline  series,  p.  218.) 

o-Toluenesulphonamide  (o-Toluenesulphamide) . — According 
to  a  patent  of  F.  v.  Heyden  Nachfolger,1  benzoylsulphon- 
imides  can  be  prepared  by  the  electrolytic  oxidation  of  toluene- 
sulphonamides  in  alkaline,  or  earthy-alkaline  solution;  for 
example,  o-benzoylsulphonimide  (benzoic  sulphimide),  or  sac- 
harin,  from  o-toluenesulphonamide: 

/S02-NH2  /S02v 

C6H4<  +30=C6H4<         >NH+2H20. 

\CH3  XCO / 

The  p-nitro-substitution  products  of  o-toluenesulphcnamide 
are  said  to  behave  similarly. 

Just  as  amines  are  easily  obtained  by  reduction  of  nitriles 
with  sodium  amalgam  or  sodium  and  alcohol,  so  this  reaction 
can  be  carried  out  electrolytically  (p.  121). 

Benzonitrile. — Ahrens,2  by  electrolytic  reduction  of  this 
substance  in  dilute  sulphuric  acid  at  a  platinum  cathode, 
obtained  benzylamine;  in  like  manner, 

Benzylcyanide  gave  the  corresponding  phenylethylamine. 

8.  THE  INDIGO  REDUCTION. 

The  reduction  of  indigo  by  electrolytic  hydrogen  in  alkaline 
suspension',  the  fluid  being  warmed,  has  already  been  carried 
out  by  Fr.  Goppelsroder  3  and  v.  Wartha.4  Mullerus  5  easily 
reduced  indigosulphonic  acid". 

Thorough  studies  regarding  the  process  of  the  reduction  of 
indigo  by  the  electric  current  have  recently  been  made  by 
A.  Binz,6  and  Binz  and  Hagenbach7;  these  show  that  most 
probably  zinc  and  not  hydrogen  plays  the  chief  part  in  the 
reduction.  Thus  when  indigo  is  electrolytically  reduced  in 

1  D.  R.  P.  No.  85491  (1895). 

2  Ztschr.  f.  Elektrochemie  3,  100  (1896). 

3  Preparation  and  Fixation  of  Dyes  with  the  Aid  of  Electrolysis,  Reichen- 
berg,  1885. 

4  Chem.  Ztg.  8,  No.  25  (1884). 
6  Ibid.  17,  1454  (1893). 

6  Ztschr.  f.  Elektrochemie  5,  5,'  103  (1898);  9,  599  (1903). 

7  Ibid.  6,  261  (1899). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.         217 

alkaline  solution,  almost  no  formation  of  indigo-white  occurs, 
but  if  alkaline-zinc  solutions  and  zinc  cathodes  are  employed 
a  smooth  reduction  (formation  of  the  vat)  takes  place. 

Binz  concludes  further  that  the  conversion  of  indigo  into 
indigo-white  depends  upon  a  withdrawal  of  oxygen  and  not 
upon  the  taking  up  of  hydrogen,  as  hitherto  supposed.  The 
phenomena  observed  in  the  reduction  of  indigo  agree  with  the 
views  regarding  the  behavior  of  attackable  cathodes,  as  men- 
tioned in  the  introduction  (p.  18).  The  reducing  agent  is  the 
discharged  zinc-ions,  whose  separation  on  the  cathode  and  whose 
reaction  with  the  depolarizer  indigo  occurs  in  a  proportion 
which  depends  upon  the  velocities  of  the  two  processes.  The 
cathode  potential  appears  as  a  measure  for  the  reduction  energy, 
whose  value  is  naturally  determined  by  the  chemical  nature 
of  the  zinc,  and  cannot  forthwith  be  attainable  by  any  other 
reducing  agent  such  as  hydrogen.  In  this  respect  we  can  say 
with  Binz  that  the  indigo  reduction  is  based  upon  the  direct 
action  of  the  metal. 

Without  entering  upon  the  subject  of  the  electrolytic  prepa- 
ration of  reducing  substances  which  are  useful  for  vat  forma- 
tion, such  as  hydrosulphites,  a  process l  of  the  Farbwerke 
Meister,  Lucius  and  Briming  in  Hochst  may  here  be  mentioned 
by  which  sulphite  solutions  are  electrolyzed  at  higher  tempera- 
tures in  the  presence  of  indigo.  Hereby  the  sulphites  are  con- 
verted into  hydrosulphites,  which  accomplish  the  reduction  of 
indigo,  the  sulphites  being  regenerated.  The  latter  are  again 
continually  reduced.  In  alkaline  electrolytes  a  vat  is  imme- 
diately formed  and  in  acid  solutions  solid  indigo-white  is  pre- 
cipitated. The  current  density  and  cathode  material  can  at 
will  be  chosen  within  wider  limits. 

9.  PYRIDINE  DERIVATIVES  AND  ALKALOIDS. 
The  pyridine  ring  is  easily  reducible.     Hydropyridines  are 
formed  from  pyridine  and  its  derivatives,  and  piperidines  by 
complete  hydratiom     Quinoline  and  acridine  are  also  easily 
converted  into  hydro-compounds. 

1  D.  R.  P.  No.  139567  (1902). 


218         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

These  reductions  can  easily  be  obtained  with  the  electric 
current  under  suitable  conditions;  the  alkaloids,  which  have  a 
pyridine  nucleus,  also  behave  analogously. 

Pyridine.  —  Ahrens  1  accomplished  the  electrolytic  reduction 
•of  pyridine  and  the  derivatives  of  pyridine,  and  obtained  piperi- 
dine  from  pyridine,  and  a-pipecoline  from  a-picoline.  In  these 
electrolyses  lead  cathodes  and  10%  solutions  of  sulphuric  acid 
were  employed. 

If  strong  sulphuric  acid  and  a  platinum  cathode  are  used 
there  is  formed  a  substance  containing  nitrogen  and  sulphur, 
the  chemical  nature  of  which  has  not  yet  been  determined. 

Benzoylpiperidine.  —  On  the  occasion  of  their  experiments  re- 
garding the  reduction  of  acid  amides,  Baillie  and  Tafel,2  by 
electrolytical  reduction  in  sulphuric  acid  at  a  lead  cathode, 
converted  benzoylpiperidine  into  benzylpiperidine  and  obtained 
.a  yield  of  77  per  cent,  of  the  latter  compound. 

Quinoline  was  electrolyzed  by  Ahrens  3  in  a  10%  sulphuric 
acid.  The  cathode  was  of  lead,  and  the  anode  of  platinum. 
An  apparently  tri-molecular  hydroquinone  (CgHgN^  was  chiefly 
formed  at  the  cathode,  besides  small  quantities  of  hydroquinoline 
(C9H9N)2  and  tetrahydroquinoline,  C9HnN2. 

According  to  a  later  patent  of  E.  Merck,4  if  quinoline 
is  electrolyzed  in  dilute  sulphuric  acid  containing  for  1  equiv- 
alent of  the  base  at  least  4  equivalents  -of  the  acid,  and  free  from 
metallic  salts,  a  good  yield  of  dihydroquinoline  is  obtained. 


C6H4 


CH\CH  /CH2\CH 


Acetyltetrahydroquinoline.  —  As  in  the  case  of  benzoylpiperi- 
dine, Baillie  and  Tafel  5  were  able  to  reduce  this  compound,  and 
obtained  a  good  yield  of  ethyl  tetrahydroquinoline. 

1  Ztschr.  f.  Elektrochemie  2,  577,  580  (1896)  ;  also  D.  R.  P.  No.  90308  (1896). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  32,  74  (1899). 

3  Ztschr.  f.  Elektrochemie  2,  580  (1893). 
4D.  R.  P.  No.  104664  (1898). 

*  Ber  d.  deutsch  chem.  Gesellsch.  32,  74  (1899). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        219 

Quinaldine  (a-methylquinoline),  according  to  the  process  of 
Ahrens,1  can  be  converted  into  dihydroquinaldine,  CioHioNH,, 
and  tetrahydroquinaldine,  CioHisN. 

The  nitroso-  and  nitro-derivatives  of  the  pyridine  and  quin- 
oline  series  have  already  been  discussed  (see  p.  192)  . 

The  coca-alkaloids,  like  cocaine,  atr  opine,  etc.,  contain  per- 
haps a  combination  of  a  piperidine  ring  with  a  pyrrolidine  ring. 
This  combination  is  also  expressed  in  their  behavior  in  electroly- 
sis. At  present  the  following  is  known. 

Atropine,  CirH^sNOs.  —  From  the  neutral  sulphate  of  atro- 
pine  crystallized  atropine  is  gradually  precipitated  at  the 
cathode,  while  at  the  anode  carbon  dioxide,  carbon  monoxide, 
oxygen,  and  nitrogen  are  evolved.  The  acid  sulphate  behaves 
in  a  similar  manner,  but  the  evolution  of  nitrogen  was  not  ob- 
served (Bourgoin2). 

Atropine  is  decomposed  by  baryta  water  into  tropic  acid  and 

Tropine. 

CH2  —  CH  —  CH2 

i     i 

CH3N       CHOH  =  C8H16NO. 
CH  — 


This  substance,  on  electrolysis  in  alkaline  and  acid  solution  at 
lead  electrodes,  and  at  a  low  temperature,  is  converted  into  tro- 
pin  one  .  3 


—  dri  —  O-H-2 

I      I 

CH3N       CO 

I         I 
CH2  —  CH  —  CH2. 

A  good  yield  of  this  substance  is    obtained.     Pseudotropine 
behaves  in  the  same  manner. 

1  Ztschr.  f.  Elektrochemie  2,  580  (1896). 

2  Bull.  soc.  chim.  12,  400  (1869). 
8D.  R.  D.  No.  118607  (1900). 


220         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Tropinone.  —  This  compound  can  inversely  be  easily  reduced 
to.  pure  tropine.  The  chem.  Fabrik  vorm.  E.  Schering1 
employs  as  electrolyte  an  aqueous  ammoniacal  ammonium  sul- 
phate solution. 

E.  Merck,2  by  electrolysis  of  a  slightly  alkaline  solution,  ob- 
tains, besides  tropine,  pseudotropine.  The  yield  is  50  per  cent. 
of  the  tropinone  employed. 

Opium  Bases. 

Opium.  —  If  opium  is  subjected  to  the  action  of  the  electric 
current,  morphine  (Ci7Hi9NO(OH)2)  goes  to  the  cathode  and 
meconic  acid  (oxypyronedicarboxylic  acid)  to  the  anode 
•(Lassaigne)  .3 

Morphine,  Ci7Hi9N03+H20.—  Pommerehne,4  by  the  elec- 
trolysis of  a  solution  of  morphine  acidified  with  sulphuric  acid, 
obtained  after  a  few  days  crystals  of  oxydimorphine  sulphate  at 
the  anode.  The  solution  became  dark-colored. 

Codeine  (methylmorphine)  Ci7Hi7NO(OH)0-CH3.  —  On 
electrolysis  of  the  neutral  sulphate  hydrogen  is  evolved,  codeine 
is  precipitated,  and  the  solution  turns  brown  (Bourgoin  5)  . 

The  acid  sulphate  undergoes  more  complete  decomposition, 
and  carbon  dioxide,  carbon  monoxide,  oxygen,  and  nitrogen  are 
split  off. 

Cotarnine,  Ci2Hi5N04  —  This  compound  is  converted  quanti- 
tatively by  the  electrolytic  hydrogen  into  pure  hydrocotarnine 
{Brandon  and  Wolffenstein  ®)  : 


Hydrastinine,  CnHisNOs,  which  does  not,  indeed,  belong  to 
the  opium  bases,  may  nevertheless  be  mentioned  here.  This  sub- 
stance is  similarly  converted  into  hydrohydrastinine,  CnHi3N02. 

1  D.  R.  D.  No.  96362  (1898). 
2D.  R.  D.  No.  115517  (1900). 

3  Tommasi,  Trait6  d'Electrochimie  788  (1889). 

4  Arch.  Pharm.  235,  364  (1897). 
8  Bull.  soc.  chim.  12,  400  (1869). 

6Ber.  d.  deutsch.  chem.  Gesellsch.  31,  1577   (1898);   D.  R.  P.  No.  94949 
(1897). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS        221 

Quina-  and  Strychnos  Bases. 

Quinine,  C2oH24N202. — Although  the  neutral  sulphate  is  a 
very  poor-  conductor,  the  acid  sulphate  is  readily  decomposed 
into  carbon  dioxide,  carbon  monoxide,  and  nitrogen.  The 
color  of  the  solution  changes  to  a  dark  brown. 

Besides  the  last-named  gases,  the  above-mentioned  alkaloids 
split  off  various  other  products,  principally  complicated  nitro- 
gen-containing compounds  (Bourgoin  l). 

Pommerehne,2  by  electrolysis  of  a  sulphuric-acid  quinine 
solution,  obtained  a  green  resinous  mass,  which  is  perhaps 
identical  with  thalleioquin  (?). 

Quinine,  cinchonine  (Ci9H22N20),  and  cinchonidine 
(Ci9H22N20),  on  electrolysis  at  lead  cathodes  in  a  50%  sul- 
phuric-acid solution,  are  converted  into  non-crystallizable 
tetrahydro-bodies  (Taf el  and  Naumann  3) . 

Strychnine,  C2iH22N202.— The  neutral  sulphate  suffers  but 
little  change.  The  solution  becomes  slightly  colored,  hydrogen 
and  oxygen  are  given  off,  and  crystals  of  strychnine  collect  at 
the  cathode. 

The  acid  sulphate  behaves  in  a  like  manner,  except  that  in 
its  case  the  formation  of  carbon  dioxide  and  carbon  monoxide,  as 
well  as  oxygen  and  nitrogen,  shows  that  a  part  of  the  substance 
undergoes  complete  decomposition.  In  strongly  acid  solutions 
the  splitting  off  of  nitrogen  does  not  occur  (Bourgoin  4) . 

Tafel  and  Naumann  5  have  made  more  thorough  investiga- 
tions regarding  the  electrolytic  reduction  of  strychnine  in  strong 
sulphuric  acid  solution  at  lead  cathodes.  According  to  TafePs 
researches,  strychnine  is  to  be  regarded  as  a  cyclical  acid  anilide 
of  the  formula: 


(C20H22ON) 


1  Bull.  soc.  chim.  12,  400  (1869). 
21.  c. 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  3299  (1901). 

4  Bull.  soc.  chim.  12, 400  (1869). 

5Lieb.  Ann.   301,  291    (1898);    Ber.  d.    deutsch.   chem.    Gesellsch.   34 
3291  (1901). 


222         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  water-soluble  tetrahydrostrychnine  is  first  formed: 

/CH2OH 

(C20H22ONK 


which  by  further  reduction  is  converted  ink)  strychnidine: 

/CH2 

(C20H22ON); 

>N 


\i 


The  quantity  of  the  former  preponderates  at  a  low  temperature. 
On  the  other  hand,  the  higher  the  temperature  the  greater  the 
quantity  of  strychnidine  formed. 

Brucine,  C23H26N204.  —  A  solution  of  the  neutral  sulphate 
turns  red  and  the  sulphate  is  decomposed.  Hydrogen  is  evolved 
at  the  negative  pole,  but  the  brucine  completely  absorbs  the 
oxygen  at  the  positive  pole  (Bourgoin). 

The  acid  salt  is  very  energetically  decomposed,  becoming 
first  red  and  then  brown.  At  the  anode  carbonic-acid  gas, 
carbon  monoxide,  oxygen,  and  nitrogen  escape  (Bourgoin1). 

Besides  the  gases  mentioned,  the  above  alkaloids  break  up 
into  other  products,  principally  complex  compounds  containing 
nitrogen. 

According  to  Tafel's  and  Naumann's2  investigations, 
brucine  behaves  like  strychnine  in  so  far  as  that  by  reduction 
under  similar  conditions  tetrahydrobrucine  is  produced;  how- 
ever, to  obtain  the  crystalline  product  the  temperature  must 
not  exceed  15°.  But  a  body  corresponding  to  strychnidine 
was  not  found  among  the  products  of  the  electrolytic  reduction 
of  brucine. 

If  we  give  brucine  the  following  formula  (Moufang  and 
Tafel3): 

/CO 

[C20H2o(OCH3)2ON}     ||    , 


•Lc. 

al.  c. 


8  Lieb.  Am.  304,  24  (1898). 


,THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        223 
then  tetrahydrobrucine  has  most  probably  the  formula: 

CH2OH 


/ 

[C20H20(OCH3)2OHj 


Brucidine,  corresponding  to  strychnidine,  is  formed  from 
tetrahydrobrucine  if  this  is  heated  to  200°,  water  being  split 
off: 

/CH2 

[C20H20(OCH3)2ON]/  |     . 
XN 

Morpholone.  —  Lees  and  Shedden  1  have  investigated  the 
electrolytic  reduction  of  pheno-  and  naphthomorpholones  in 
sulphuric-acid  solution.  Morpholines  are  produced  only  as 
by-products,  the  morpholone  ring  being  for  the  most  part 
broken  up. 


Phenomorpholone,  C6H 

NH/co2 

gives  as  end-products  of  the  reduction  acetyl-o-aminophenol, 

OH 


C6H 

NHCOCH3; 


also  ethyl-o-amino  phenol, 


/OH 


\NHCH2CH3, 
and  also  isoacetyl-o-aminophenol, 

\N  =  C(OH)CH3. 

1  Proceed.  Chem.  Soc.  Id,  132  (1903);  Journ.  Chem.  Soc.  83,  750  (1903) 


224         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 
n-Methylphenomorpholone, 

x/°\CH2 

4\N/co' 

CH3 

gives,  besides  n-acetylmethyl-o-aminophenol, 

XDH 


C6H 
and  n-methylethyl-o-aminophenol, 


also  n-methylphenomorpholine, 

/°\CH2 

C6H4<         |       . 

\NXCH2 

CH3 

n-Methyl-/?-naphthomorpholone       gives       n-methylethyl-a 
amino-/?-naphthol  : 


and  n-methyl-/?-naphthomorpholine  : 

'°\CH 


H6<          |     . 
\N/CH2 


CH3 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        225 


10.  THE  CAMPHOR  GROUP. 

Camphor.  —  This  substance,  as  shown  ,by  the  synthesis  car- 
Tied  out  by  Romppa,1  has  certainly  the  formula  proposed  by 
Bredt: 

CH3- 
CH2  -  C  ---  CO 

CH3CCH3 

I 

CH2  -  CM  -  CIi2 

Being  a  ketone  it  can  be  reduced  to  the  secondary  alcohol 
borne  ol: 

CH3 
CH2  -  C  --  CH(OH) 

I  I 

CH3CCH3 


This  reduction  has  been  carried  out  electrolytically  by  Tafel 
and  Schmitz  2  in  sulphuric-acid  solution  at  mercury  catnodes. 
They  obtain  thus  about  45  per  cent,  of  the  theoretically  possible 
yield,  with  a  maximum  current  consumption  of  38  per  cent. 
At  lead  cathodes  no  satisfactory  reduction  can  be  effected. 

Camphoric  Acid, 

CH3 
CH2  -  C—  -  COOH 


CH3CCH3 


COOH 


is  the  oxidation  product  of  camphor  with  nitric  acid. 

Brown  and  Walker 3  also  electroylzed  (see  p.  102)  the 
sodium-ethyl  salt  of  camphoric  acid  and  obtained  two  esters 
which  they  were  able  to  separate  by  means  of  fractional  dis- 

1  Ber.  d.  deutsch.  chem.  Gesellsch.  36,  4332  (1903). 

2  Ztschr.  f.  Elektrochemie  8,  288  (1902). 
»  Lieb.  Ann.  274,  71  (1893). 


226         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

tillation.  One  of  these  (boiling-point  212°-213°)  on  being 
saponified  yielded  an  unsaturated  monobasic  acid,  CgH^C^, 
campholytic  acid;  the  other  having  a  higher  boiling-point 
(240°-242°),  was  the  neutral  ester  of  a  diabasic  acid,  Ci8H3o04, 
to  which  Walker  gave  the  name  of  camphothetic  acid.  These 
experiments  are  of  great  importance,  because  they  prove  the 
dibasic  nature  of  camphoric  acid,  a  fact  which  was  doubted 
by  Friedel. 

Walker  and  Henderson 1  found,  moreover,  that  upon 
electrolysis  of  concentrated  aqueous  solutions  of  the  ethyl- 
potassium  salt  of  allocamphoric  acid  there  are  formed  as  chief 
products  the  ethyl  esters  of  a  dibasic  acid,  Ci6H28(COOH)2,. 
and  of  a  monobasic  acid,  C8Hi3COOH: 


/COOC2H5  /COOC2H5 

=2C02+C16H28<; 
XCOO  XCOOC2H5 


1.  2C8H14<  =2C02+Ci6H28^ 

XCOO 

,COOC2^5 

2.  2C8Hi4<'  =  C8Hi4^ 

XCOO  XCOOH 

+C02+C8H13COOC2H5. 

It  has  been  found  on  further  investigation  2  that  besides  the 
strongly  dextrorotary  unsaturated  acid  designated  as  allocam- 
pholytic  acid,  C8Hi3COOH,  an  isomeric  acid  is  formed  which, 
although  slightly  dextrorotary  as  obtained,  is  perhaps  even 
laevorotary  in  an  entirely  pure  condition.  The  latter  on  being 
heated  to  200°  splits  off  carbon  dioxide  and  yields  a  hydrocarbon, 
C8Hi4,  which  boils  at  120-122°  and  appears  to  be  identical  with 
laurolene, 

CH2-CK 


CH2-C(CH3)2 

made  from  camphoric  acid. 

A  ketbnic  acid,  C8Hi30-COOH,  melting-point  228°,  is  also 
found  as  an  additional  product  of  the  electrolysis  of  potassium 


1  Journ.  Chem.  Soc.  67,  337  (1895). 

2  Ibid.  69,748  (1897). 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        227 

allocamphoric  ethyl  ester.    The  authors  concluded  from  their 
observations  that  camphoric  acid  contains  the  group 

H 

~9\COOH 
-C-COOH, 

a  deduction  which  had,  of  course,  to  be  later  modified. 

According  to  later  experiments  of  Walker  and  Cormack,1  it 
is  possible  to  obtain  isolauronolic  acid  by  electrolyzing  the 
methyl-ester-potassium  salt  of  camphoric  acid: 

/COOCH3  /COOCH3 

2C8H14<  =  C8H14<  +C02 

XCOO  XCOOH 

+C8H13COOCH3. 

The  free  optically  inactive  isolauronolic  acid, 
CH2—  CCOOH 

II 
CH3C 

/CHs 


2  —  C 

CH3, 

was  obtained  from  the  latter  ester.     The  electrolytic  reaction 
occurs  hence  in  a  normal  direction. 
Camphoric-acid  imide, 

CH3 
CH2—  C  --  CO 

I 
CH3CCH3  >NH 

I 
CH2—  CH—  CO 

was  reduced  in  sulphuric-acid  solution  at  a  prepared  lead 
cathode.  The  experiment  was  made  by  Tafel  and  Eckstein,2 
in  connection  with  their  investigations  concerning  the  electro- 

1  Proceed.  Chem.  Soc.  16,  58  (1900). 

2Ber.  d.  deutsch.  chem.  Gesellsch.  34,  3274  (1901);    see  also  D.  R.  P 
No.  126195  (1900). 


228         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 


lytic  reduction  of  succinimide  (p.  119).  Just  as  succinimide,  by 
replacement  of  one  of  the  two  oxygen  atoms  by  two-  hydrogen 
atoms,  is  converted  into  pyrrolidone  and,  by  complete  elimina- 
tion of  the  oxygen,  into  pyrrolidine — although  only  to  a  very 
slight  extent — so  camphoric-acid  imide  gives  two  perfectly 
analogous  products,  camphidone  and  camphidine. 

Camphidone  occurs  in  two  isomeric  modifications,  separable 
in  the  form  of  the  picrates,  a-camphidone  and  /9-camphidone : 


CH3 
CH2-C 


NH     and 


CH 
CH2 —  C  — 

I 
CH3CCH3 

CH2—  CH-CO 


Which  one  of  these  is  the  a-  and  which  the  /2-camphidone 
remains  undecided. 
Camphidine, 

CH3 
CH2—  C  —  CH2 


CH3CCH3 

I 
CH2-  CH-CH2- 


>NH, 


is  always  produced  besides  camphidones,  and  can  be  readily 
separated  from  these,  since  it  possesses  a  decidedly  basic  char- 
acter. 

As  the  camphidones  are  extremely  resistant  towards  further 
reduction,  they  form  no  intermediate  phase  in  the  camphidine 
formation.  We  must  suppose  that  only  those  acid-imide 
molecules,  both  of  whose  carboxylic  groups  are  by  accident 
simultaneously  attacked  by  the  reducing  agent,  are  changed  into 
camphidine.  Or,  a  carbinol-like  intermediate  product,  in 
which  the  second  carboxylic  group — in  contradistinction  to 
that  of  camphidone— is  electrolytically  attackable,  is  already 
formed  during  the  transition  from  camphoric-acid  imide  to  the 
camphidone. 


THE  ELECTROLYSIS  OF  AROMATIC  COMPOUNDS.        229 

11.  ELECTROLYSIS  OF  BLOOD  AND  ALBUMEN. 

Blood.1 — The  defibrinated  blood  of  a  dog  was  submitted  to 
electrolysis  by  Becquerel.  He  made  use  of  platinum  electrodes 
and  a  current  furnished  by  a  battery  of  three  Daniell  cells.  At 
the  negative  pole  he  observed  the  following  phenomena: 

The  blood  became  brown  and  alkaline,  and  contained 
neither  white  nor  red  corpuscles;  it  possessed  the  property  of 
gradually  dissolving  blood-corpuscles  and  had  the  odor  of  putrid 
meat. 

At  the  positive  pole  undecomposed  and  partially  decomposed 
blood-corpuscles  were  present  in  large  quantities.  The  fluid 
gave  a  precipitate  of  albumen  with  nitric  acid,  mercuric  chlo- 
ride and  lead  acetate. 

Albumen.2 — When  an  albumen  solution  was  electrolyzed  by 
Dumas  and  Prevost,  under  conditions  similar  to  those  used  by 
Becquerel  for  blood,  the  alkali  metal  went  to  the  negative  pole, 
hydrogen  was  evolved,  and  acetic  and  phosphoric  acids  appeared 
at  the  positive  pole.  The  result  of  this  is  that  the  albumen  is 
coagulated  at  the  negative  pole  (by  the  alkali  present),  while  at 
the  positive  pole  the  solution  remains  clear. 

As  Lassaigne  has  shown,  pure  albumen  in  aqueous  solution 
is  a  non-conductor  of  electricity;  the  addition  of  salts  or  acids 
is  therefore  necessary  in  its  electrolysis. 

The  Pharmaceutical  Institute  of  L.  W.  G^ns  of  Frankfurt 3 
has  made  known  a  process  for  electrochemically  preparing 
fluorine-substitution  products  of  albumens.  The  latter  are 
suspended,  or  dissolved  in  a  dilute  aqueous  solution  of  hydro- 
fluoric acid  or  salts  of  this  acid,  and  subjected  at  a  platinum 
electrode  to  the  anode  current  action.  The  discharged  fluorine 
reacts  with  the  albumen,  forming  substitution  products. 

1  Tommasi,  Traite  d'Electrochimie  800  (1889). 

21.  c. 

3D.  R.  RNo.  116881  (1898). 


CHAPTER  V. 
ELECTROLYSIS  WITH  ALTERNATING  CURRENTS. 

IF  the  polarity  of  the  current  is  not  allowed  to  change  too 
rapidly,  it  is  possible,  since  oxidation  and  reduction  occur  suc- 
cessively at  each  pole,  to  accomplish  electrolyses  with  alternat- 
ing currents.  Experiments  with  this  end  in  view  have  been 
made  by  Drechsel.1  Dehydration  is  a  case  of  simultaneous 
reduction  and  oxidation.  The  supposition  that  in  living  organ- 
isms carbamide  is  produced  from  ammonium  carbamate  by  the 
splitting  off  of  water  prompted  Drechsel  to  make  experiments  in 
this  direction.  When  an  aqueous  solution  of  ammonium  'car- 
bamate is  electrolyzed  with  a  current  from  a  battery  of  4-6 
Grove  cells,  and  platinum  electrodes  used,  carbamide  is  obtained 
independently  of  the  electrode  material  when  alternating  currents 
are  employed.  The  reactions  are  supposed  to  be  either 

I.  NH2COONH4+  0  =  NH2COONH2  +  H20, 
II.  NH2COONH2+2H  =  NH2CONH2  +  H20, 
or 

I 
II. 


The  observation  that  the  platinum  electrodes  were  strongly 
attacked,  with  the  formation  of  platinum  salts,  caused  Gerdes  2 
to  investigate  the  platinum  bases.  As  the  principal  product  he 
found  a  compound  to  which  he  gave  the  following  formula  : 

XONH3  ,       XNH3NH30 
C0<  [  Pt< 

\ONH3  J      XNH3NH3 

1  Journ.  prakt.  Chem.  22,  476  (1880);  Ber.  d.  deutsch.  chem.  Gesellsch. 
13,  2436  (1880). 

2Journ.  prakt.  Chem.  26,  257  (1882);    see  also  Inaug-Dissert.,  Leipzig 

1882. 

230 


ELECTROLYSIS  WITH  ALTERNATING  CURRENTS.        231 
and  the  chloride  of  which  is  said  to  have  the  composition 
C1NH3\        /NH3NH3C1 


3\  /i 

>Pt<( 

[/   N 


PtCl4+2H20. 
C1NH/       XNH3NH3C1' 


Gerdes  also  examined  the  nitrate  and  sulphate  of  this  base. 

In  the  course  of  further  researches  1  Drechsel  found  that 
when  alkaline  solutions  were  used  platinum  was  present  in  the 
electrolyzed  fluid.  Copper  when  used  as  electrode  showed  a 
similar  behavior;  lead  was  less  attacked,  gold  but  very  slightly, 
and  palladium  not  at  all. 

The  formation  of  phenylsulphuric  acid  in  living  organ- 
isms is  supposed,  like  carbamide,  to  be  the  result  of  dehydra- 
tion. Taking  this  into  consideration,  Drechsel  carried  out  the 
following  experiment: 

A  saturated  solution  of  acid  magnesium  carbonate  was  mixed 
with  an  equal  volume  of  a  solution  of  magnesium  sulphate  and 
the  mixture  was  saturated  with  commercial  carbolic  acid. 

When  this  solution  was  electrolyzed  for  thirty  hours  with 
alternating  currents,  using  platinum  electrodes,  then  the  follow- 
ing products  were  obtained: 

1.  f-Diphenol.  7.  Succinic  acid. 

2.  Pyrocatechin.  8.  Malonic  acid  (?). 

3.  Hydroquinone.  9.  n- Valeric  acid  (?). 

4.  Phenylsulphuric  acid.  10.  n-Butyric  acid  (?). 

5.  Oxalic  acid.  11.  Some     cyclohexanone,2 

6.  Formic  acid.  CeHioO. 

According  to  Drechsel  the  formation  of  the  phenol  ester  of 
sulphuric  acid  is  probably  represented  by  the  following  equa- 
tions : 

I.  C6H5OH  +  HOS03H  +  0  =  C6H5OOS03H  +  H20, 

Later  Drechsel 2  electrolyzed  normal  caproic  acid  with  alter- 
nating currents.  The  electrolytic  solution  contained,  in  a  vol- 

1  Journ.  prakt.  Chem.  29,  229  (1884). 

2  Ibid.  84,  135  (1886). 


232         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

ume  of  3  liters,  200  g.  of  caproic  acid  as  magnesium  salt  and 
was  nearly  saturated  with  acid  magnesium  carbonate.  Plati- 
num electrodes  were  used.  At  the  end  of  the  experiment  the 
following  compounds  could  be  identified  in  the  solution  : 

1.  Valeric  acid.  5.  Adipic  acid. 

2.  Butyric  acid.  6.  Oxycaproic  acid. 

3.  Oxalic  acid.  7.  Glutaric  acid. 

4.  Succinic  acid. 

In  a  still  later  research  on  the  electrolysis  of  phenol  with 
alternating  currents  Drechsel  1  detected  phenylsulphuric  acid, 
dioxybenzenes,  a  number  of  acids  of  the  fatty  acid  series,  and 
in  addition  to  these  an  oil  which  he  identified  as  hydropheno- 
ketone, 

CH2 

H2C      C:0 

I 

CH.2 


and  whose  phenylhydrazine  compound  he  was  able  to  isolate. 
Drechsel  regards  hydrophenoketone  as  the  origin  of  the 
fatty  compounds  formed.  By  the  direct  addition  of  water  to 
this  compound  caproic  acid  results,  and  this  then  breaks  up 
into  the  acids  and  other  "decomposition  products  mentioned 
above. 

Some  of  the  above  acids  have  been  mentioned  as  decompo- 
sition products  of  phenol  in  the  investigation  cited  on  the  elec- 
trolysis of  phenol. 

1  Journ.  pract.  Chem.  38,  65  (1888). 


CHAPTER  VI. 
ELECTRIC  ENDOSMOSE. 

BY  electric  endosmose  or  cataphoresis  is  meant  the  often 
observed  phenomenon  of  the  migration  or  flow  of  a  fluid,  under 
the  influence  of  potential  differences,  through  the  diaphragm 
separating  the  cathode  and  anode  chambers.  This  flow  or  trans- 
portation of  fluid  always  occurs  in  a  certain  direction,  either 
to  the  anode  or  to  the  cathode,  depending  upon  the  nature 
of  the  substances  and  the  diaphragm;  it  has  no  connection 
with  the  electrical  phenomena  following  Faraday's  laws.  If 
the  rigid  diaphragm  is  replaced  by  fine  suspensions  which  act 
like  a  movable  diaphragm,  the  fluid  remains  at  rest,  but  the 
suspended  particles  migrate,  i.e.,  are  urged  in  the  fluid  towards 
the  electrode.  This  directed  movement  depends  undoubtedly 
upon  a  polar  charge  of  the  suspended  particles  contrary  to  that 
of  the  water.  Since  the  organic  colloids,  like  the  colloid  solutions 
of  albumen,  carbohydrates,  haemoglobin,  indigo,  and  of  natural 
dyes,  act  as  an  extremely  fine  suspension,  cataphoresis  alsa 
possesses  great  importance  for  organic  substances,  as  to  their 
suspension,  coagulation  and  sedimentation  phenomena.  The 
scientific  treatment  of  this  field  has  begun.  Bredig 1  mentions 
that  the  direction  of  albumen  depends  upon  the  chemical  com- 
position of  the  fluid;  for  instance,  whether  the  aqueous  medium 
is  alkaline  or  acid. 

Electric  endosmose  is  of  technical  importance  for  the' 
dehydration  of  organic,  finely  suspended  substances  containing 
very  much  water,  for  example,  the  drying  of  peat,  according; 

1  Ztschr.  f.  Elektrochemie  9,  739  (1903). 

233 


234         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

to  the  experiments  of  Schwerin.1  The  peat,  at  a  tension  of 
4  to  5  volts  per  centimeter  peat  layer,  migrates  to  the  anode 
and  is  deposited  on  the  latter  in  a  firm  coat,  while  at  the  cathode 
the  water  becomes  clear.  Aqueous  dye-pastes  behave  simi- 
larly. The  technical  purification  of  albumens  by  cataphoresis 
is  also  said  to  be  feasible. 

Another  field  in  which  cataphoresis,  or  the  convective  con- 
duction as  the  process  is  also  called,  has  apparently  already 
become  of  great  importance,  is  the  tanning  industry. 

If  the  skin  to  be  tanned  is  brought  between  the  cathode 
and  anode  in  a  dilute  tannic-acid  solution,  a  migration  of  the 
colloidally  dissolved  tannic  acid  takes  place  through  the  skin 
from  the  positive  to  the  negative  electrode.  By  a  regular 
slow  change  of  the  current  direction  the  tannic-acid  solution 
can  be  pressed  into  the  pores  of  the  skin  and  thus  a  considerable 
saving  in  time  is  accomplished.2 

Note. — It  has  been  known  for  a  long  time  that  many  finely 
divided  bodies  suspended  in  water,  as  gold,  copper,  graphite, 
silica,  feldspar,  sulphur,  lycopodium,  etc.,  as  well  as  minute  drops 
of  liquids,  such  as  €82  and  oil  of  turpentine,  and  bubbles  of 
oxygen,  marsh-gas,  etc.,  show  cataphoresis  phenomena.  All 
these  are  urged  in  water  towards  the  positive  electrode,  but  in 
oil  of  turpentine  the  direction  is  reversed  except  in  the  case  of 
particles  of  sulphur;  the  direction  is  also  reversed  for  silica  in 
carbon  disulphide.  The  earlier  experiments  along  these  lines  on 
solid  particles  contained  in  fluids  of  high  resistance  were  made 
by  Faraday,  Jiirgensen,  Quincke,  etc. — Translator. 

1  Ztschr.  f.  Elektrochemie  9,  739  (1903);    D.  R.  P.    No.   131932   (1901). 

2  S.  Foelsing,  Jahrb.  d.  Elektrochemie  2,  269  (1895). 


PART  II. 

ELECTROTHERMIC   PROCESSES   AND    THE   SILENT 
ELECTRIC  DISCHARGE. 


CHAPTER  I. 
THEORETICS  AND  METHODICS. 

1.  THEORETICS. 

ACCORDING  to  Ohm's  law  the  strength  or  intensity  of  the 
electric  current,  i.e.  the  quantity  of  electricity  which  is  con- 
ducted by  an  electric  conductor  or  a  system  of  conductors 
in  a  given  time,  is  directly  proportional  to  the  effective  electro- 
motive force,  and  inversely  proportional  to  the  resistance 
of  the  current  field: 


where  i  is  the  current  strength,  e  the  electromotive  force  or 
the  tension,  and  w  the  resistance.  The  work  which  elec- 
trical energy  can  perform  in  a  current  field  is  expressed  by 
the  product  of  the  electromotive  force  existing  in  this  field 
and  the  current  strength 

A  =  e  •  i, 

where  A  denotes  the  work  to  be  done. 

Substances  are  known  which  interpose  a  more  or  less  strong 
resistance  to  the  passage  of  the  current,  and  such  whose  resist- 

235 


236         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

ance  is  so  great  that  practically  no  passage  of  the  current 
takes  place.  The  former  are  called  conductors  of  electricity; 
the  latter  non-conductors  or  insulators.  The  conductors 
themselves  are  in  turn  again  subdivided  into  two  sharply 
defined  classes;  those  which  conduct  the  current  without 
being  materially  changed,  i.e.  the  passage  of  electricity  pro- 
duces no  change  in  the  chemical  composition  of  the  substance, 
and  those — presenting  a  remarkable  contrast  to  the  former — 
in  which  the  passage  of  electricity  results  in  the  chemical 
decomposition  of  the  substance  of  the  conductor  at  points 
where  the  electric  current  enters  and  leaves  the  body,  i.e. 
changes  of  the  substance  occur.  To  the  former  class  of  con- 
ductors belong  all  metals  and  carbon,  the  conductors  of  the 
first  class;  to  the  latter  the  bases,  acids,  and  salts  in  solution, 
particularly  aqueous  solution,  or  in  a  molten,  and  also,  under 
certain  conditions,  in  a  solid,1  state.  They  form  conductors 
of  the  second  class,  or  electrolytes. 

Ohm's  law  is  equally  applicable  to  both  classes.  The 
work  which  the  current  can  do,  however,  depends  upon  the 
nature  of  the  conductor.  If  the  circuit  is  completely  metallic 
and  closed,  the  total  electric  energy  can  be  converted  into 
heat;  but  if  the  circuit  contains  an  electrolyte,  a  large  part 
of  the  electric  energy  is  used  up  in  the  production  of  chemical 
and  physical  effects  which  occur  when  the  circuit  is  closed. 

To  determine  in  a  simple  way  the  connection  of  the  electric 
•energy  with  the  calorific  energy  caused  by  it,  an  electric  cir- 
cuit can  be  closed  by  a  metallic  wire  placed  in  a  calorimeter, 
and  the  current  measured  calorifically  by  the  heat  effects 
produced  by  the  different  electromotive  forces  and  intensi- 
ties. The  result  of  such  measurements  is  the  equivalence  of 
the  heat  occurring  in  the  conductor  with  the  electric  energy, 
lience  with  the  product  of  electromotive  force  into  the  electric 

quantity 

Q  =  kei, 

where  Q  denotes  the  heat  generated  in  the  wire.    The  factor  k 

is  the  electrical  equivalent  of  heat,  which  permits  a  numerical 

1  See  Nernst,  on  "solid  electrolytes,"  Zeit.  f.  Elektrochemie  6,  41-43  (1899). 


THEORETICS  AND  METHODICS.  237 

comparison   of  the   two  forms   of  energy.    It   follows,   that 
0.239  cal  =  l  voltxl  coulomb. 

If  we  introduce  from  Ohm's  law  the  factor  iw  for  the  elec- 
tromotive force  e,  then 

Q  =  k-  i2w. 

The  amount  of  heat  generated  in  a  given  time  varies  directly 
as  the  product  of  the  resistance  of  the  conductor  into  the 
square  of  the  current  strength.  This  relation  is  called  Joule's  1 
law,  named  after  its  discoverer.  The  heat  which  is  thus  derived 
only  from  the  current  quantities,  but  not  from  chemical  changes, 
is  also  called  Joule's  heat. 

If,  besides  the  metallic  connections,  an  electrolyte  is  included 
in  the  closed  circuit,  a  part  of  the  electric  energy  is  used  up 
in  chemical  work.  The  electrical  energy  is  then  transformed 
in  various  ways, — in  all  parts  of  the  current  field  heat  is 
developed  proportional  to  the  resistance  of  each  separate 
part  and  the  square  of  the  current  strength,  but  chemical 
work  and  material  changes  and  disarrangements  in  the  elec- 
trolyte are  also  accomplished. 

In  utilizing  the  heat  produced  by  the  current  for  reactions  of 
organic  bodies,  only  those  systems  are  taken  into  account  in 
which  the  current,  by  forming  a  spark  discharge  or  luminous 
arc,  is  forced  either  to  pass  through  gases  or  vapors  with  high 
resistance,  or  to  heat  wires  or  filaments  to  high  temperatures. 
While  the  extremely  high  temperatures,  which  can  be  attained 
by  means  of  the  voltaic  arc  in  the  electric  furnace,  have  through 
Moissan's  investigations  become  of  great  importance  for  mineral 
chemistry,  it  is  a  peculiarity  of  organic  substances,  whose  con- 
ditions of  existence,  with  few  exceptions,  are  connected  with 
relatively  low  temperatures,  and  are  mostly  quite  sensitive, 
that  the  methods  applicable  here  must  allow  a  fuller  scope  in 
temperature  than  is  accorded  by  the  spark  discharge  or  luminous 
arc.  RuhmkorfFs  coils,  and  less  often  frictional  electric  machines, 

'Phil.  May  19,  260  (1841). 


238         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

are  usually  employed  for  giving  sparks.  The  resistance  fur- 
naces, in  which  a  tube  of  carbon  is  heated  by  the  current,  seem 
more  suited  for  carrying  out  pyrogenic  reactions  of  carbon  com- 
pounds. Both  heating  methods  have  already  been  used.  Lep- 
sius  1  has  employed  the  luminous  arc  for  decomposing  gases  and 
demonstrating  volumetric  proportions,  also  for  preparing  water 
gas.  Bredig2  made  some  qualitative  tests  on  the  behavior  of 
separate  organic  fluids  towards  the  luminous  arc,  while  Hofmann 
and  Buff  3  have  also  investigated  the  effect  of  electrically  incan- 
descent platinum  and  iron  wires  on  some  gases  and  vapors. 
Legler,4  in  his  experiments  on  the  incomplete  combustion  of 
ether,  also  employed  electrically  heated  platinum.  Moreover, 
Haber,5  by  making  the  heated  conductor  (of  platinum,  plati- 
num-iridium,  or  carbon)  tube-shaped  and  conducting  the  cur- 
rent of  gas  through  the  hollow  centre  in  which  was  placed  a 
glass  or  porcelain  tube,  perfected  the  principle  of  resistance 
ovens  for  the  chemical  investigations  of  gases.  But  these  in- 
vestigations did  not  lead  to  an  extensive  use  of  these  electrical 
methods  for  obtaining  pyrogenic  reactions  with  organic  bodies. 
Most  of  the  material  of  such  reactions  has  so  far  been  collected 
with  the  spark  discharge  between  metallic  electrodes;  of  late 
years  numerous  experiments  on  the  pyrogenic  reactions  of  or- 
ganic bodies  have  been  undertaken  with  electrically  incandes- 
cent wires  or  filaments. 

2.  THE  REACTION  TEMPERATURES. 

Before  taking  up  the  subject  of  the  individual  results,  some 
remarks  on  the  attainable  temperatures,  the  possibility  of  their 
variation,  their  measurement  and  calculation  will  be  made. 

No  very  accurate  measurements  of  the  temperatures  occur- 
ring in  the  spark  discharged  are  available,  great  difficulties 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  23,  1418,  1637,  1642  (1890). 

2  Ztschr.  f.  Elektrochemie  4,  514  (1898). 
3 Lieb.  Ann.  113,  129  (I860). 

4  Ibid.  217,  381  {1883);   Ber  d.  deutsch.  chem.  Gesellsch.  18,  3350  (1885). 
6  Experimental    Investigations    on  the  Decomposition  and  Combustion 
of  Hydrocarbons  (Munich,  1896)  43. 


THEORETICS  AND  METHODICS.  239 

being  encountered  in  their  determination.  Calorific  methods 
are  best  suited  for  investigating  the  temperature  of  the  lumi- 
nous arc,  or  the  radiant  energy  is  employed  for  learning  the 
temperature.  In  the  latter  case  a  bolometer  or  photometer 
is  used. 

According  to  Violle,1  the  temperature  of  the  positive  car- 
bon point  and  of  the  carbon  particles  in  the  voltaic  arc  equals 
the  evaporation  temperature  of  carbon.  This  was  determined  by 
breaking  off  the  incandescent  tip  of  the  carbon  and  dropping  it 
into  a  calorimeter.  One  gram  carbon  requires  1600  cal.  to  heat 
it  from  0°  up  to  its  evaporation  temperature.  As  300  cal.  are 
necessary  to  heat  it  from  0°  to  1000°,  1300  cal.  remain  for  raising 
the  temperature  from  1000°  to  x°,  if  x  is  the  evaporation  tem- 
perature of  carbon.  If  we  take  the  specific  heat  of  carbon 
at  0.52,  then  1300  cal.  represent  2500°  more,  so  that  the  evapo- 
ration temperature  of  carbon,  x,  and  the  hottest  parts  of  the 
luminous  arc,  equal  35000.2 

Langley,  Paschen,  Violle,  and  Le  Chatelier2  sought  to 
determine  the  temperature  of  the  heated  body  by  means  of 
the  radiant  intensity. 

The  use  of  the  thermopile  in  the  form  of  Le  Chatelier's3 
platinum,  platinum-rhodium  thermocouple,  a  so-called  pyrom- 
eter, has  obtained  especial  importance.  This  can  be  used  to 
measure  temperatures  up  to  17000.4  The  electromotive  force  is 
measured  either  by  one  of  the  well-known  methods,  or  else  direct 
reading  precision-voltmeters  (or  galvanometers),  whose  scales  are 
divided  both  into1  millivolts  and  into  the  corresponding  degrees 
Celsius  or  Fahrenheit,  are  employed.  The  determination  of  the 

1  Compt.  rend.  115,  1273  (1892);  119,  949  (1894). 

2  Barus,  Die  physik.  Behandlung  und  die  Messung  hoher  Temperaturen, 
Leipzig,  1892;    also  Bredig,  Uber  die  Chemie  der  extremen  Temperaturen, 
Leipzig,  1901. 

3  Le  Chatelier  et  Boudouard,  Mesure  des  temperatures  elevens,  Paris, 
1900.  Le  Chatelier,  Compt.  rend.  114,  470   (1892)  etc.   Holborn  u.  Wien. 
Ann.  56,  360  (1895);   59,  213  (1896);   Holborn  u.  Day,  Wied.  Ann.  G8,  820 
(1899),  etc. 

4  Wanner's  Optical  Pyrometer  indicates  up  to  4000°  C.     See  Journ.  Am. 
Chem.  Soc.,  1904. 


240         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

temperature  from  the  electromotive  force  is  based  upon  the 
fact  that  on  heating  the  joint  where  the  platinum  wire  is  fused 
to  the  platinum-rhodium  wire,  an  electromotive  force  of  about 
one  millivolt  for  every  100°  C.  is  produced.  The  ratio  of  the 
electromotive  force  to  the  temperature  of  the  fused  joint 
is  accurately  determined  by  the  Physik-tech.  Reichsanstalt, 
and  the  result  accompanies  the  calibrated  pyrometer.  The 
data  always  refer  to  an  arrangement  whereby  the  connections 
between  the  thermocouple  and  the  conducting  wires  are  at  0°, 
while  the  fused  joint  of  the  couple  is  placed  in  the  space 
whose  temperature  is  to  be  measured. 

The  resistance  thermometer  1  is  .  extremely  convenient  for 
measuring  wide  ranges  of  temperature.  The  electric  resistance 
of  pure  metals  increases  with  the  temperature  about  0.4% 
per  degree  (C.);  but  the  temperature  coefficient  for  different 
metals  and  also  for  different  temperature  intervals  is  by  no 
means  constant.2  If  the  temperature  coefficient  is  known, 
for  accurate  purposes  the  resistance  during  the  experiment 
can  be  measured  with  a  Wheatstone  bridge;  for  less  accurate 
measurements  it  will  often  be  sufficient  to  determine  the  ten- 
sion of  the  incandescent  wire  and  the  intensity  in  the  current 
circuit,  and  to  calculate  the  resistance  according  to  Ohm's 
law.  Care  must,  however,  be  taken  that  the  conducting  wires 
connected  with  the  wire  whose  temperature  is  being  inves- 
tigated are  practically  without  resistance.  For  showing  the 
dependence  of  the  resistance  upon  the  temperature  an  equa- 
tion of  the  following  form  usually  suffices: 


or 


The  values  a,  6,  and  c,  or  a,  /?,  and  7-  are  given  in  the  tables. 
Pyrogenic  reactions,  whose  course  remains  the  same  within 

1  Holborn  and  Wien,  Wied.  Ann.  56,  383  (1895);   59,  213  (1896).     Cal- 
lendar,  Phil.  Mag.  32,  104  (1891). 

2  Landolt-Bornstein,  Physik.-Chemische  Tabellen. 


THEORETICS   AND  METHODICS.  241 

larger  temperature  intervals,  permit  of  a  further  simplification, 
naturally  at  the  cost  of  accuracy.     If  we  make 

wt  =  w0(l+at), 

in  which  the  range  of  the  respective  temperature  must  be  con- 
sidered in  the  choice  of  a,  then 


a-w0  ' 

a  is  for  iron  about  0.0045,  for  nickel  0.0036,  for  platinum 
0.0033,  and  for  platinum-iridium  (20%  iridium)  0.00105,  all 
metals  in  wire  shape.  This  approximate  determination  is 
convenient,  even  if  pyrogenic  reactions  are  brought  about  by 
the  wire  itself,  whereby  an  accurate  determination  of  reaction 
temperature  often  becomes  illusory  for  the  most  various  reasons.1 

3.  ARRANGEMENTS. 

Little  can  be  said  about  the  arrangements  to  be  chosen  for 
the  pyrogenic  reactions  of  organic  bodies.  Both  the  spark 
discharge  and  the  luminous  arc  can  be  produced  in  fluids  or 
molten  substances.  Lob,2  in  decompositions  with  the  luminous 
arc,  employed  a  small  flask  with  three  tubulures,  about  the 
shape  and  size  of  the  boiling-vessel  employed  in  Beckmann's 
method  for  determining  molecular  weights.  Each  of  the  two 
side  tubes  of  equal  dimensions  supports  a  thin  carbon  rod 
passed  through  the  perforation  of  a  tightly  fitting  stopper, 
so  that  the  electrodes  in  the  inside  of  the  vessel  are  at  an  angle 
to  one  another.  The  centre  tubulure  supports  a  return  con- 
denser to  which  is  attached  an  arrangement  for  collecting  the 
generated  gases.  By  regulating  the  volume  of  the  liquid  in 
the  decomposition  flask,  the  luminous  arc  can  at  will  be  pro- 
duced in  the  liquid  or  its  vapor.  In  the  latter  case  the  sub- 
stance is  heated  to  boiling  and  the  circuit  closed  as  soon  as  the 
air  in  the  apparatus  is  displaced  by  the  vapor. 

1  Lob,  Ztschr.-f.  Elektrochemie  7,  903  (1901). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  915  (1901). 


242         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  degree  of  decomposition  by  the  voltaic  arc  depends 
of  course,  to  a  great  extent  upon  the  chemical  nature  of  the 
liquids  and  vapors  in  which  the  luminous  arc  is  produced. 
While  ether,  methyl  alcohol,  ethyl  alcohol,  glacial  acetic  acid, 
and  other  aliphatic  fluids  and  their  vapors  are  subject  to  decom- 
positions with  very  trifling  charring,  and  give  products  which  are 
chemically  closely  related  to  the  products  started  with,  benzene, 
toluene,  nitrobenzene,  aniline,  naphthalene,  phenol,  and  other 
members  of  the  aromatic  series  are  destroyed,  and  considerable 
charring  results. 

For  this  reason  the  method  worked  out  and  employed  by 
Lob,1  replacing  the  luminous  arc  by  metallic  and  carbon  re- 
sistances, proves  in  general  to 
be  more  suitable  for  the  pur- 
pose of  obtaining  pyrogenic  re- 
actions of  organic  substances. 

A  round  flask  with  a  long 
neck  is  closed  with  a  thrice- 
perforated  stopper.  Two  small 
glass  tubes  with  strong  platinum 
hooks  sealed  in  the  lower  ends 
are  passed  through  the  two  side 
perforations;  a  little  mercury 
forms  the  connection  between 
the  hooks  and  the  conducting 
wires  leading  in.  Or,  strong 
wires  bent  into  hooks  at  one  end 
are  directly  stuck  through  the 
stopper,  which  can  be  done  with- 
out injuring  the  tight  fit.  The  incandescent  wire,  a  metallic  wire 
of  about  0.2  mm.  diameter,  is  fastened  to  the  hooks  by  wrapping 
it  around  or  hooking  it  on.  A  return  condenser  is  placed  in 
the  centre  perforation.  Lob,  when  making  decompositions  in  a 
perfectly  air-tight  apparatus  and  under  diminished  pressure, 
replaces  the  stopper  by  a  ground-glass  stopper  in  which  the 


FIG.  8. — Electropyrogenizer. 


1  Lob,  Ztschr.  f.  Elektrochemie  7,  904  (1901);  10,  505  (1904). 


THEORETICS  AND  METHODICS.  243 

small  tubes  with  platinum  hooks  are  sealed  in.  The  return 
condenser,  which  serves  as  an  internal  cooling  apparatus, 
is  attached  to  the  side;  another  glass  tube  sealed  in  the  wall 
of  the  flask  (not  shown  in  the  figure)  serves  for  admitting  air, 
or  for  the  passage  of  other  gases  for  special  purposes  (see 
Fig.  8).  This  apparatus  is  particularly  adapted  for  pyrogenic 
reactions  of  high-boiling  substances  in  a  partial  vacuum.  The 
substance  is  placed  in  the  round  bulb.  Direct  heating  converts 
it  into  vapor,  which,  after  the  air  has  been  removed,  is  per- 
manently in  contact  with  the  incandescent  wire. 


CHAPTER  II. 
THE  SPARK  DISCHARGE  AND  THE  VOLTAIC  ARC. 

1.  THE  SPARK  DISCHARGE. 

It  is  well  known  that  most  of  the  gaseous  hydrocarbons  of 
the  aliphatic  series  when  exploded  with  an  excess  of  oxygen  are 
.converted  into  the  end-products  of  combustion,  carbonic  acid 
and  water.  This  fact  is  made  use  of  in  quantitative  gas  analysis. 
The  combustion  is  often  not  complete;  intermediate  products 
can  be  obtained  if  we  start  with  hydrocarbon  derivatives  instead 
of  the  hydrocarbons  themselves. 

Berthelot  gave  a  comprehensive  exposition  of  the  results 
known  at  that  time  on  the  effect  of  the  spark  discharge  upon 
the  formation  and  decomposition  of  carbonic  acid  and  hydro- 
carbons and  the  herewith  occurring  equilibrium  phenomena 
(Berthelot,  Essai  de  Mecanique  Chimique  II,  336-362,  Paris, 
1879). 

Methane. — The  induction  sparks  decompose  this  substance 
into  carbon  and  hydrogen  (Hofmann1  and  Buff),  which  fact 
Dalton  had  already  observed. 

Berthelot 2  obtained  hydrogen,  carbon  and  acetylene.  If 
the  latter  is  continually  gotten  rid  of,  the  greater  part  of  methane 
can  be  converted  into  acetylene,  otherwise  the  latter  is  decom- 
posed and  changed  in  a  complex  manner. 

Methane  is  also  produced  by  the  reaction  of  carbon  monoxide 
with  hydrogen  under  the  influence  of  the  induction  spark 

1  Lieb.  Ann.  113,  129  (1860). 

2  Ibid.  123,  211  (1862). 

244 


THE    SPARK    DISCHARGE    AND    THE  VOLTAIC  ARC.    245 

(Brodie  1),  a  fact  which  explains  the  formation  of  hydrocyanic 
acid  from  carbon  monoxide,  hydrogen,  and  nitrogen,  as  will 
be  mentioned  further  on. 

Ethylene  is  decomposed  by  the  spark  discharge  into  its 
elements  (Dalton,  Hofmann,  and  Buff2).  According  to  Wilde,3 
acetylene  is  first  formed,  and  is  then  decomposed  into  its 
elements.  Besides,  according  to  Thenard  and  Berthelot,4  a 
fluid  and  solid  product  are  produced. 

W.  G.  Mixter  5  has  recently  investigated  the  combustion 
phenomena  of  several  hydrocarbons  by  means  of  a  weak  electric 
spark  discharge,  and  has  proven  among  other  things  that 
ethylene  can  also  yield  acetic  acid  besides  carbonic  acid.  The 
pressure  under  which  the  gases  react  is  important  for  the  course 
of  the  experiment.  Mixter  sought  to  determine  the  relative 
reaction  velocities  as  compared  with  that  of  an  oxyhydrogen 
mixture,  under  equal  conditions. 

Acrolem,  CH2:CH-CHO,  according  to  E.  von  Meyer,6  is 
formed  when  ethylene  with  an  excess  of  oxygen  is  exploded  in 
a  eudiometer. 

Formic  Acid. — Wilde  7  found  that  the  action  of  the  electric 
spark  on  gaseous  mixtures  of  oxygen  and  alcohol,  hydrogen  and 
carbon  dioxide,  and  methane  and  carbon  dioxide,  produced 
formic  acid.  In  the  first  and  last  mentioned  of  these  mixtures 
acetic  acid  is  also  formed. 

Acetylene. — The  spark  acts,  as  already  mentioned,  by 
reason  of  its  high  temperature  which,  according  to  Berthelot,8  is 
sufficient  to  produce  acetylene  from  a  mixture  of  carbon  disul- 
phide  and  hydrogen,  sulphur  being  precipitated. 


'•  Lieb.  Ann.  169,  270  (1873). 

2  Ibid.  113,  129(1860). 

3  Ztschr.  f.  Chemie  2,  735  (1866). 

4  TraitS  de  M6canique  chimique  II,  350  (1879). 

5  Ann.  Journ.  of  Sc.  [4]  4,  51  (1897);  Journ.  Chem.  Soc.  73,  246  (1898); 
Proceed.  Chem.  Soc.  39  (1898). 

6  Journ.  f.  prakt.  Chemie  [2]  10,  113  (1874). 

7  Bull.  soc.  chim.  [2]  5,  267  (1866). 

8  Tommasi  Traite  d'Electrochimie  715  (1879). 


246         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Hydrocyanic  Acid.  —  Berthelot 1  obtained  this  substance 
by  passing  the  electric  spark  through  a  mixture  of  acetylene  and 
nitrogen.  The  acid  is  in  fact  frequently  produced  in  far- 
reaching  decompositions  by  the  electric  spark;  thus  from  a 
mixture  of  ethylene  or  aniline  vapor  with  nitrogen  (Berthelot J), 
from  a  mixture  of  acetylene  with  nitric  oxide  (Huntington  2), 
ammonia  with  benzene,  or  ether  and  nitrogen  (Perkin3),  etc. 
The  reactions  are  also  in  a  certain  sense  reversible.  Hydrocyanic 
acid  is  readily  split  up  by  the  current  (Gay-Lussac  4),  and  in  the 
presence  of  hydrogen  (Berthelot  5),  into  acetylene  and  nitrogen. 

The  union  of  acetylene  and  nitrogen  to  .hydrocyanic  acid 
takes  place  rather  smoothly  if  the  easy  decomposability  of 
acetylene  is  lessened  by  dilution  with  hydrogen,  as  was  already 
done  by  Berthelot.6  His  experiments  were  recently  again 
taken  up  by  Gruszkiewicz.7  The  electrodes  were  blackened  by 
a  deposition  of  carbon  except  with  a  maximum  content  of 
acetylene  of  5  per  cent,  by  volume  (composition  of  tne  gas 
mixture:  5  per  cent,  acetylene,  5  per  cent,  nitrogen  and  90  per 
cent,  hydrogen). 

Gruszkiewicz  obtained  better  results  by  using  a  mixture  of 
carbon  monoxide,  hydrogen,  and  nitrogen.  He  found  that  the 
proportion  of  the  components  was  essentially  decisive  for  the 
yield  and  the  reaction  velocity.  A  mixture  approximately  cor- 
responding in  composition  to  that  of  water  gas,  Dowson  gas, 
generator  gas,  etc.,  gave  encouraging  results.  Thus,  if  3  liters 
of  a  gas  mixture  of  54.62  per  cent.  CO,  24.88  per  cent.  N2,  and 
20.50  per  cent.  H2  were  permitted  to  flow  for  an  hour  through 
the  space  through  which  the  sparks  were  discharged,  then  about 
12  cc.  hydrocyanic  acid  were  obtained.  Carbon  dioxide,  like 
carbon  monoxide,  is  reduced  by  hydrogen  in  the  spark  dis- 


1  Bull.  soc.  chim.  [2]  13,  107  (1869). 

2  D.  R.  P.  No.  93852  (1895). 

8  Jahresb.  f.  Chemie.  399  (1870). 

4  Ann.  chim.  phys.  78,  245  (1811);  Gilberts  Ann.  1811. 

6  Bull.  soc.  chim.  [2]  13,  107  (1869). 

e  Traite  de  Mecanique  chimique  II,  355  (1879). 

7  Ztschr.  f.  Elektrochemie  9,  83  (1903). 


THE    SPARK    DISCHARGE    AND    THE  VOLTAIC    ARC.     247 

charge,  and  changed,  by  uniting  with  nitrogen,  into  hydrocyanic 
acid.     The  reaction  can  be  shown  in  the  equation, 

2CO+3H2+N2=2HCN+2H20; 
or,  2CO+6H2=2CH4+2H20 

2CH4+N2=2HCN+3H2. 

Cyanogen  shows  the  same  easy  decomposability  as  hydro- 
cyanic acid.  Both  Berthelot 1  and  Hof mann  and  Buff  2  ob- 
served that  cyanogen  was  decomposed  into  its  elements  by  the 
action  of  the  electric  spark.  The  least  trace  of  water  in  the 
gas  caused  the  formation  of  hydrocyanic  acid  and  acetylene. 

The  observation  of  Morrens,3  who  claimed  to  have  obtained 
cyanogen  in  an  atmosphere  of  nitrogen  by  passing  the  induction 
spark  between  two  carbon  electrodes,  is  therefore  incorrect. 
The  decomposition  of  cyanogen  by  the  action  of  .the  electric 
spark  has,  moreover,  been  noted  by  Davy,  and  by  Andrews 
andTait.4 

Ethyl  Alcohol. — In  an  atmosphere  of  ethyl-alcohol  vapors, 
M.  Quet  5  and  Perrot  6  obtained,  besides  some  carbon,  a  sub- 
stance which  exploded  on  being  heated,  the  chemical  nature  of 
which  they  were  unable  to  determine.  The  liquid  became  acid 
but  Perrot  found  that  no  water  was  formed  in  the  decomposi- 
tion of  the  alcohol;  he  was  also  unable  to  prove  the  presence 
of  carbonic  acid  gas.  Melly  7  and  Lommel 8  made  similar  ex- 
periments, the  latter  employed  a  Holtz  machine.  The  gas 
escaping  in  the  decomposition  of  the  alcohol  probably  contains 
acetylene  and  ethylene. 

Ethyl  Ether. — According  to  Wilde's 9  experiments,  ethyl 
ether,  under  reduced  pressure,  also  yields  ethylene  besides  other 

1  Compt.  rend.  82,  1360  (1876). 

2  Lieb.  -Ann.  113,  129  (1860). 

3  Compt.  rend.  48,  342  (1859). 

4  Journ.  Chern.  Soc.  13,  344  (1861). 
6  Compt.  rend.  46,  903  (1858). 

6  Ibid.  46,  180  (1858);  47,  351  (1859). 

7  Tommasi,  Traite  d'Electrochimie,  724  (1879). 

8  Ibid.,  725  (1879). 

8  Ztschr.  f.  Chemie  2,  735  (1866). 


248         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

gases,  and  a  deposition  of  carbon.  Truchot 1  observed  methane 
and  hydrogen  besides  the  ethylene.  Perrot,2  by  the  action  of 
bromine  upon  the  gases  obtained  by  the  action  of  the  electric 
spark,  was  able  to  isolate  a  liquid,  C3H5Br3,  boiling  at  135°- 
140°,  and  isomeric  with  tribromhydrin.  Klobukow,3  by  heat- 
ing ether  vapor  to  250°-300°  and  passing  the  spark  through 
the  latter,  obtained  carbon  monoxide,  hydrogen,  methane,  ethyl- 
ene, and  acetylene. 

Acetone. — Wilde  4  investigated  the  action  of  the  electric 
spark  on  acetone  vapor  in  a  Torricelli  vacuum.  Acetylene  was 
formed  in  the  gas  mixture  and  carbon  was  deposited  on  the 
sides  of  the  vessel. 

Formic  Acid,  on  the  contrary,  does  not  yield  acetylene 
(Wilde).  Nor  could  he  prove  the  presence  of  this  gas  in  the 
decomposition  of  acetic  acid. 

Methylamine. — The  electric  spark,  when  passed  through 
methylamine  vapor  by  Hofmann  and  Buff,5  gave  primarily  hydro- 
gen and  methylamine  hydrocyanide ;  further  action  brougnt  about 
complete  decomposition,  tarry  substances  being  deposited. 

Trimethylamine  was  investigated  by  the  same  authors.  It 
also  is  completely  broken  up,  tarry  products  being  formed. 

Ethylamine. — Hofmann  and  Buff  obtained  tar-like  products 
and  a  non-alkaline  gas  having  an  odor  like  that  of  ethyl  cyanide. 

The  experiments  carried  out  on  the  behavior  of  compounds 
of  the  aromatic  series  when"  subjected  to  the  electric  spark  have 
so  far  given  very  few  results. 

Benzene. — Destrem6  investigated  the  action  of  the  induc- 
tion spark  between  two  platinum  points  on  benzene,  and  ob- 
tained a  gas  mixture  of  acetylene  and  hydrogen,  while  the  liquid 
contained  diphenyl  and  a  crystalline  substance  which  was  not 
closely  investigated  Benzene  vapor,  under  reduced  pressure, 

1  Compt.  rend.  84,  714  (1877). 
Ibid.  46,  180  (1858). 

Journ.  f.  prakt.  chemie  [2]  34,  126  (1886). 
Bull.  soc.  chim.  [2]  5,  267  (1866). 
Lieb.  Ann.  113,  129  (1860). 
Bull.  soc.  chim.  42,  267  (1884). 


THE    SPARK    DISCHARGE    AND    THE  VOLTAIC  ARC.    249 

is  decomposed  by  the  electric  spark,  likewise  producing  acetyl- 
ene (Wilde2). 

Toluene.— Destrem 1  obtained  from  toluene,  as  from  ben- 
zene, acetylene,  and  hydrogen.  The  liquid  contained,  besides 
diphenyl,  a  solid  substance  which  was  not  further  investi- 
gated. 

Naphthalene. — Wilde2  also  investigated  the  behavior  of 
naphthalene  vapor  under  reduced  pressure  when  subjected  to- 
the  action  of  the  induction  spark.  He  obtained  a  gas  mixture 
containing  acetylene. 

Aniline. — Destrem3  investigated  the  action  of  the  electric 
spark  from  an  induction  apparatus  on  aniline  vapor,  and 
observed  a  decomposition  into  acetylene,  hydrogen,  hydro- 
cyanic acid,  and  nitrogen. 

Pyrogenic  reactions  of  organic  compounds  with  the  "' electric 
flame/'  (flaming  discharge)  as  produced  at  a  lower  tension  and 
higher  intensity  than  required  for  the  production  of  the  spark 
(at  about  2000-4000  volts  and  0.05-0.15  amp.)  have  not  yet. 
been  carried  out. 

According  to  the  investigations  of  W.  Muthmann  and  H. 
Hofer,4  interesting  results  are  also  to  be  expected  in  its  appli- 
cation to  organic  compounds. 

2.  THE  VOLTAIC  ARC. 

As  already  mentioned  in  the  introduction,  the  enormously 
high  temperature  of  the  luminous  arc  is  only  applicable  in 
certain  cases  to  organic  compounds. 

Several  reactions  have,  however,  become  of  fundamental, 
theoretical  and  practical  importance;  for  instance,  Berthelot's 
acetylene  synthesis,  the  preparation  of  carbides,  and  some 
other  processes. 

1  Bull.   soc.  chim.   42,  267  (1884). 

2  Ibid.  5,  267  (1866). 

3 1.  c.,  see  also  Jahresb.  f.  Chem.  272  (1884). 
4  Ber.  d.  deutsch.  cfcem.Gesellsch.  36,  438  (1903). 


250         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Acetylene. — Berthelot1  showed  that  carbon  and  hydrogen 
combined  to  acetylene  on  passing  the  voltaic  arc  over  carbon 
points  in  an  atmosphere  of  hydrogen.  The  synthesis  of  acety- 
lene from  its  elements  first  made  possible  the  complete  syn- 
thesis of  a  whole  series  of  organic  compounds.  Acetylene,  as 
is  well  known,  is  produced  by  the  decomposition  of  many 
organic  compounds  at  high  temperatures.  Bredig2  thus 
obtained  acetylene,  besides  other  hydrocarbons,  when  he  pro- 
duced the  luminous  arc  in  liquid  petroleum. 

The  Metal  Carbides. — These  are  of  great  technical  and  scien- 
tific importance.  They  have  been  repeatedly  and  thoroughly 
described,  hence  a  reference  to  various  works  upon  this  subject 
will  suffice  here.3 

Bolton4  succeeded  in  combining  chlorine  and  carbon.  He 
employed  the  voltaic  arc  ^between  carbon  electrodes  in  an  at- 
mosphere of  chlorine.  Perchlorethane  is  principally  produced; 
hexachlorbenzene  is  formed  in  lesser  quantity.  As  both  of  these 
chlor-hydrocarbons  are  produced  by  the  complete  chlorination 
of  carbon  tetrachloride,  Bolton  assumes  their  intermediate 
existence;  the  intermediate  occurrence  of  gaseous  or  fluid 
compounds -like  perchlorethylene  does  not  seem  improbable. 
Bromine  and  iodine  appear  to  react  analogously  (Bolton4); 
experiments  with  the  latter  halogens  yet  await  a  scientific 
treatment.  They  would  undoubtedly  prove  remunerative. 

Lob  5  has  made  several  other  decompositions  by  means  of 
the  voltaic  arc  between  carbon  points.  These  were  carried  out 
with  the  following  vapors  and  liquids : 

Methyl  Alcohol  yields  formic  acid,  and  also  about  39  per  cent, 
methane,  45  per  cent,  hydrogen,  small  quantities  of  carbonic 

1  Ann.  chim.  phys.  [4]  13,  143  (1868);    see  also  Berthelot:    Essai  de  M6- 
canique  Chimique  II,  332-336  (1879). 

2  Ztschr.  f.  Elektrochemie  4,  514  (1898). 

3Moissan,  The  Electric  Furnace,  Ahrens:  Die  Metallkarbide  (Sammlung 
chemisch-technischer  Vortrage),  Stuttgart,  1896,  Haber:  Grundriss  der  tech- 
nischer  Elektrochemie,  Miinchen  und  Leipzig,  1898.  See  also,  "  Recent  liter- 
ature on  carbides,"  Journ.  Am.  Chem.  Soc.  1904,  p.  200.— Trans. 

4  Ztschr.  f.  Elektrochemie  8,  165  (1902);  9,  209  (1903). 

5  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  915  (1901). 


THE  SPARK    DISCHARGE    AND    THE    VOLTAIC  ARC.    251 

acid,  carbon  monoxide,  and  acetylene.  Formaldehyde  is  not 
formed. 

Glacial  Acetic  Acid  yields  about  35  per  cent,  carbon  monoxide, 
26  per  cent,  hydrogen,  15.5  per  cent,  carbonic  acid,  and  12  per 
cent,  saturated  and  7  per  cent,  unsaturated  hydrocarbons. 

Benzene. — The  benzene  is  colored  brown  and  is  considerably 
charred;  no  substance  could  be  isolated  from  the  liquid.  The 
escaping  gas  consists  of  86-90  per  cent,  hydrogen  as  well  as 
small  quantities  of  saturated  and  unsaturated  hydrocarbons. 

Naphthalene  likewise  yields  chiefly  hydrogen,  the  residue 
being  greatly  charred. 

Cyanogen  is  completely  decomposed  by  the  voltaic  arc,  as 
shown  by  Hofmann  and  Buff.1 

Cyanides. — The  attempts  to  prepare  cyanides  by  the  direct 
or  indirect  union  of  nitrogen  and  carbon  must  be  mentioned 
here;  they  are  of  importance  particularly  for  the  problem  of 
utilizing  atmospheric  nitrogen.  Since  the  reactions  take  place 
at  a  high  temperature,  we  can  also  make  use  of  electrically  pro- 
duced heat,  as  suggested  by  Readmann;2  but  in  his  process — 
a  mixture  of  oxides  or  carbonates  of  alkalies,  or  earthy  alkalies, 
with  carbon  is  heated  in  the  voltaic  arc  between  two  carbon 
points  in  the  presence  of  nitrogen — electrolysis  occurs  as  an 
important  factor.  The  conditions  are  similar  in  his  attempts, 
undertaken  with  Gilmour,3  to  prepare  potassium  ferrocyanide. 


1  Lieb.  Ann.  113,  129  (1860). 

2  Eng.  Pat.  No.  6621  (1894). 

3  Eng.  Pat.  No.  24116  (1892). 


CHAPTER  III. 

THE  UTILIZATION   OF  CURRENT  HEAT  IN  SOLID 
CONDUCTORS. 

Methane. — Davy  decomposed  methane  with  an  electrically 
incandescent  platinum  wire  into  carbon  and  hydrogen,  an 
effect  which  was  also  later  obtained  by  Hofmann  and  Buff 1 
with  an  electrically  incandescent  iron  spiral. 

Ethylene,  according  to  the  last  named  investigators,1  like- 
wise breaks  down,  under  similar  conditions,  into  its  elements. 

Cyanogen. — Cyanogen  also  is  completely  split  up  by  an 
incandescent  iron  wire  into  carbon  and  nitrogen. 

Haber  2  has  made  some  experiments  regarding  the  decompo- 
sition of  several  hydrocarbons  in  the  electric  furnace.  The  gas 
current  was  conducted  through  a  glass  or  porcelain  tube  which 
was  placed  in  an  electrically  heated  tube  of  platinum,  platinum- 
iridium,  or  carbon. 

Hexane. — No  considerable  decomposition  of  hexane  vapor 
occurs  at  about  600°;  at  800°-940°,  however,  there  were  pro- 
duced the  following  percentages  of  gases,  based  on  100  per  cent, 
of  the  vaporized 'hydrocarbon: 

Methane 27.77% 

Olefines  (ethylene).  ...  22. 14% 

Acetylene 1.00% 

Hydrogen 2.44% 

Benzene 6.76-10% 

Carbon 3.27% 

Tar 29.22% 

1  Lieb.  Ann.  113,  129  (1860). 

2  Experimental-Untersuchungen  iiber   Zersetzung  und  Verbrennung  von 
Kohlenwasserstoffen,  43-77  Munich  (1896). 

252 


CURRENT  HEAT  IN  SOLID  CONDUCTORS.  253 

At  a  still  higher  temperature  hexane  is  for  the  greater  part 
converted  into  its  elements. 

Trimethylethylene  is  split  up  at  930°-940°  in  the  following 
manner.  From  100  per  cent,  of  material  started  with  there 
were  obtained. 

Methane 27.72% 

Ethylene 8.10% 

Hydrogen 1.76% 

Gaseous  by-products.  . .  .    4.46% 

Acetylene 0.30% 

Carbon 5.09% 

Benzene 8.00-13.41% 

Tar 33.71-39.12% 

The  above  figures  represent  percentages  by  weight.  At 
1000°  trimethylethylene  is  also  extensively  decomposed. 

Ethyl  Ether. — For  obtaining  a  slow  combustion  of  the  ether, 
Legler  1  passed  a  mixture  of  ether  vapor  and  air  over  an  elec- 
trically incandescent  platinum  wire  and  obtained  a  mixture 
of  formic  acid,  acetic  acid,  formaldehyde,  acetaldehyde,  and 
hexaoxymethylene  peroxide  (CH^COGOaH-SH^O. 

Lob  has  recently  carried  out  a  great  number  of  pyrogenic 
reactions  and  syntheses,  employing  the  already  described 
arrangement  (p.  242)  with  electrically  incandescent  metallic 
wires  and  carbon  filaments. 

Methyl  Alcohol.2 — On  employing  a  cherry-red  incandescent 
iron  wire,  this  substance  yielded,  besides  formic  acid  and  a 
little  trioxymethylene,  a  gas  mixture  containing  about  72 
per  cent,  hydrogen,  20  per  cent,  carbon  monoxide,  6.5  per  cent, 
methane,  and  traces  of  carbon  dioxide.  The  figures  represent 
percentages  by  volume,  the  same  as  below. 

Chloroform.3 — This  compound,  when  brought  into  contact 
with  an  incandescent  wire  of  iron,  nickel,  platinum,  or  platinum- 
iridium  heated  to  850°-950°,  is  decomposed,  there  being  formed 
perchlorbenzene  (10%),  perchlorethane  (12%),  and  perchlor- 

1  Ber.  d.   deutsch.  chem.  Gesellsch.  18,  3350  (1885). 

2  Ibid.  34,  917  (1901). 

3  Ztschr.  f.  Elektrochemie  7,  903  (1901). 


254         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

ethylene  (30%).  The  figures  refer  to  percentages  by  volume 
based  on  the  original  material.  Much-  hydrochloric  acid  is 
also  produced,  and,  after  the  passage  of  the  gases  through 
water,  a  small  quantity  of  carbon  monoxide.  If  a  mixture  of 
chloroform  with  water  is  subjected  to  a  similar  pyrogenic  decom- 
position, a  good  deal  of  carbon  monoxide  is  evolved.  Its 
formation  is  to  be  explained  by  the  intermediate  presence  of 
dichlormethylene. 

Chloroform  and  Aniline.1—  The  vapors  of  these  two  sub- 
stances, blown  with  steam  against  the  incandescent  metallic 
wire,  unite  chiefly  to  triphenylguanidine,  while  decomposition 
products  of  chloroform  alone,  perchlorbenzene,  perchlorethane 
and  perchlorethylene,  are  present  in  considerably  smaller  quan- 
tities. The  formation  of  triphenylguanidine  is  easily  under- 
stood by  supposing  that  dichlormethylene  is  intermediately 
produced.  Phenylisocyanide  is  primarily  formed  from  this 
substance  and  aniline;  the  isocyanide  immediately  takes  up 
chlorine,  which  is  derived  from  the  accompanying  process, 
3C2C14  =  C6C16  +  3C12,  and  unites  further  with  the  excess  of  aniline 
to  triphenylguanidine  : 


II. 
III.  C6H5NCC12  +  2C6H5NH2  =  CeHsNCtHNCeHs)  2  +  2HC1. 

On  the  basis  of  these  experiments  Lob  arranges  the  follow- 
ing scheme  for  the  pyrogenrc  chloroform  decomposition,  which 
affords  a  complete  expression  of  all  the  observed  phenomena  : 

CC13H  --  >CC12 

I 


1  Ztschr.  f.  Elektrochemie  7,  903  (1901). 


CURRENT  HEAT  IN  SOLID  CONDUCTORS.  255 

The  arrows  show  the  direction  and  the  possible  reversibility 
of  the  reactions;  stable  end-products  are  printed  in  heavy  type. 

Carbon  Tetrachloride.1  — This  compound,  when  decomposed 
alone  by  an  arrangement  similar  to  that  used  for  chloroform, 
gives  off  great  quantities  of  chlorine ;  perchlorbenzene,  perchlor- 
ethane  (in  very  trifling  quantity),  and  perchlorethylene  are 
also  produced.  The  presence  of  water  in  this  case  also  increases 
the  yield  of  carbon  monoxide.  Aniline  leads  to  tripihenyl- 
guanidine,  some  resin  being  also  formed. 

The  scheme  of  decomposition  for  tetrachlormethane  is  the 
following : 

CC14- 

I 
C2C14< 


If  air  is  blown  simultaneously  with  the  tetrachlormethane 
vapors  against  the  incandescent  wire,  there  is  produced  phos- 
gene, which  is  probably  formed  by  direct  oxidation  of  dichlor- 
methylene  : 

CC12  +  0  =  CC120. 


Perchlorethylene2  yields  a  gas  mixture  of  chlorine  and  a 
little  carbon  monoxide,  and  also  phosgene  in  the  presence  of  air. 
The  residue  in  the  flask  consists  principally  of  perchlorbenzene 
besides  traces  of  perchlorethane.  Addition  of  water  consider- 
ably increases  the  quantity  of  carbon  monoxide. 

Chloral  Hydrate,3  when  subjected  to  pyrogenic  decomposi- 


M.  c. 

3  Ztschr.  f.  Elektrochemie  10,  504  (1904). 


256         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

tion  alone  or  mixed  with  water  vapors,  breaks  up  in  the  same 
manner.    The  reactions  are  expressed  in  the  following  scheme : 

C  C13CHO  -  --» CC12 +C1HCO 

cici4  ^ 

HC1  +  CO 


Besides  the  products  observed  in  the  decomposition  of 
chloroform,  carbon  monoxide  also  occurs  as  a  direct  decomposi- 
tion product  of  the  unstable  formylchloride. 

Trichloracetic  Acid  is  completely  decomposed  at  higher 
temperatures  into  gases;  Joist l  could  detect  hydrochloric  acid, 
chlorine,  carbon  monoxide,  and  carbon  dioxide,  besides  traces 
of  phosgene.  The  decomposition  takes  place,  perhaps  with  the 
aid  of  moisture,  as  shown  in  the  equation : 

2CC13COOH  +  H20  =  C12  +  4HC1  +  SCO  +  C02. 

Phosgene  is  formed  secondarily  from  chlorine  and  carbon 
monoxide. 

Acetyl  Chloride  breaks- up  (Joist x)  completely  into  approx- 
imately equal  volumes  hydrochloric  acid,  carbon  monoxide,  and 
unsaturated  hydrocarbons  (mostly  ethylene).  The  reaction 
is  expressed  in  the  equation: 

2CH3COC1  =  2HC1  +  2CO  +  C2H4. 

Bromoform  splits  off  hydrobromic  acid  and  some  free  bro- 
mine, and  yields  as  chief  product  perbromethylene,  also  per- 
brom  benzene  (Joist l).  Hexabromethane  occurs  only  in  traces; 
this  was  to  be  expected  on  account  of  its  easy  decomposability 
into  bromine  and  perbromethylene.  Some  carbon  monoxide 

1  The  experiments  have  not  yet  been  published.     Bonn  (1904). 


CURRENT  HEAT  IN  SOLID  CONDUCTORS.  257 

escapes.  If  the  bromoform  vapors  are  mixed  with  aqueous 
vapors  the  products  remain  the  same;  but  no  gas  is  evolved, 
and  the  water  contains,  besides  hydrobromic  acid,  small  quan- 
tities of  formic  acid.  The  following  expresses  the  decomposition : 

CBr3H  — 

1 
C2Br4  <-~-^^ 

'~  C2Br6 


Presence  of  water  determines  the  reaction: 

CBr  2  +  2H20  =  HCOOH  +  2HBr, 
while  with  chloroform  the  reaction  is 

CC12  +  H20  =  CO+2HC1, 

carbon  monoxide  being  produced. 

Benzene,  as  is  well  known,  is  easily  converted  at  high 
temperatures  into  diphenyl  and  complex  hydrocarbons.  Lob's 1 
method  is  very  well  suited  for  preparing  diphenyl  on  a  small 
scale.  Metallic  wires  serve  the  same  purpose  as  carbon  filaments. 
Diphenylbenzene  occurs  as  a  by-product  in  small  quantity. 

Nitrobenzene,  blown  in  vapor  form  against  the  incandescent 
wire,  decomposes  violently,  sometimes  explosively,  producing 
a  charred  mass  and  large  quantities  of  nitric  oxide.  The  reaction 
is  moderated  by  diluting  the  vapors  with  aqueous  vapor,  but 
the  obtainable  products  are  so  complex  that  their  determination 
has  not  yet  been  accomplished  (Lob  2). 


1  Ztschr.  f.  Elektrochemie  8,  777  (1902). 

2Ber.  d.  deutsch.  chem.  Gesellsch.  34,  918  (1901);    Ztschr.  f.  Elektro- 
chemie 8,  775  (1902). 


258         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

o-Nitrotoluene.  —  Although  the  pure  vapors  of  o-nitrotolu- 
ene  behave  like  those  of  nitrobenzene,  o-nitrotoluene  diluted 
with  aqueous  vapors  yields  anthranilic  acid,  in  addition  to  a 
little  o-cresol  and  salicylic  acid  and  considerable  resinous  sub- 
stances (Lob  *)  .  It  is  possible  that  ant  hr  anil  is  primarily  formed 
from  o-nitrotoluene,  water  being  split  off;  the  anthranil  is  then 
converted  into  anthranilic  acid  by  the  highly  heated  steam, 

just  as  by  boiling  with  alkalies: 

t 

/N02  /Nv 

C6H4<(         =C6H4     |/0  +  H20. 

\CH3 


The  presence  of  salicylic  acid  must  evidently  be  referred 
to  the  action  of  the  hot  aqueous  vapors  upon  anthranilic  acid: 

/NH2  /OH 

C6H4<  +  H20  =  C6H4<  +  NH3. 

XCOOH  XCOOH 

Slight  traces  of  ammonia  could  be  detected.  The  o-cresol 
was  evidently  formed  from  o-nitrotoluene  and  aqueous  vapor, 
with  splitting  off  of  nitrous  acid. 

The  material  of  the  glower  is  mostly  without  any  influence 
on  the  reaction.  Platinum,  platinum-iridium,  .  nickel,  iron 
and  carbon  gave  qualitatively  equal  results;  only  copper 
wires  are  not  applicable  for  the  preparation  of  anthranilic 
acid.  They  primarily  cause  a  reduction  to  o-toluidine  and 
then  complete  combustion  is  brought  about  by  the  copper 
oxide  which  is  formed. 

Aniline.2  —  This  compound  is  colored  brown,  ammonia  is 
split  off  and  some  gas  evolved.  Diphenylamine  and  car- 
bazole  could  be  isolated. 

Diphenylamine.2  —  On  conducting  the  vapors  of  this  sub- 
stance mixed  with  those  of  chloroform  over  metallic  glowers, 


1  Ztschr.  f.  Elektrochemie  8,  776  (1902). 

2  Ber.  d.  deutsch.  chem.  Gesellsch.  34,  918  (1901) ;   Ztschr.  f.  Elektro- 
chemie 7,  913  (1901). 


CURRENT  HEAT  IN  SOLID  CONDUCTORS. 


259 


diphenylamine  combines  with  chloroform  and  gives  a  small 
yield  of  acridine. 

Benzyl  Chloride,  benzol  chloride  and  benzotrichloride,  when 
subjected  like  chloroform  to  pyrogenic  decomposition,  behave 
quite  like  the  latter  compound;. a  dissociation  into  hydro- 
chloric acid,  or  chlorine  and  phenylmethylene,  or  chlorphenyl- 
methylene,  seems  to  occur  first  (Lob1). 

Benzal  Chloride  gives  smoothly  stilbene,  with  splitting  off 
of  hydrochloric  acid: 

2C6H5CH2C1  ->  2C6H5  •  CH  +  2HC1 

I 
CgHs  •  CH '  CH  •  CgHs. 

Benzal  chloride  also  splits  off  hydrochloric  acid,  but  no 
chlorine;  a  mixture  of  a-  and  /9-tolane  dichlorides  results: 

2C6H5  •  CHC12 >  2C6H5  •  CC1  +  2HC1 


•  I 
C6H5  CC1 

C6H5  CC1 


i 
C6H5  CC1 

C1C  C6H5 


Benzotrichloride  at  first  gives  off  chlorine,  which  does  not, 
however,  escape,  but  is  absorbed  by  a  part  of  the  primarily 
formed  tolane-dichlorides;  these  are  thereby  converted  into 
tolanetrichloride  and  tetrachloride. 

2C6H5  •  CC13 >  2C6H5  •  CC1  +  2C12 


C6H5-CC1 
C6H5  CC1 


C6H5  CC1 


C6H5  CC1 
C6H5  CC12 

C6H5  CC12 

•  cci2 


1  Ber.  d.  deutsch.  chem.  Gesellsch.  36,  3059  (1903);    Ztschr.  f.  Elektro- 
chemie  9,  903  (1903). 


260         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

If  a  mixture  of  benzotrichloride  and  water  is  subjected 
to  pyrogenic  decomposition,  the  yield  of  tolane  dichlorides, 
tri-  and  tetrachlorides  is  very  small,  although  these  substances 
do  not  entirely  disappear.  Benzaldehyde  and  benzoic  acid 
become  the  chief  products.  The  benzaldehyde  is  apparently 
the  reaction  product  of  chlorphenylmethylene  with  water,  and 
the  benzoic  acid  the  oxidation  product  of  the  benzaldehyde  by 
the  intermediately  occurring  chlorine.  Benzalchloride,  in  the 
presence  of  water,  gives  benzaldehyde;  no  benzoic  acid  is 
formed. 


CHAPTER  IV. 

THE  SILENT  ELECTRIC  DISCHARGE  AND    THE    ACTION   OF 
TESLA-CURRENTS. 

I.  THE  SILENT  ELECTRIC  DISCHARGE. 

WHILE  the  action  of  the  induction  spark  upon  organic 
bodies,  gases  and  vapors  is  undoubtedly  a  thermic  process,  in 
the  silent  electric  discharge  the  electric  energy  plays  a  more 
important  part,  either  as  such  or  in  the  form  of  radiant  energy. 
In  this  case  we  are  dealing  with  a  constant  passage  of  an  electric 
current  through  gases.  Even  if  the  theory  of  the  conduction 
in  gases  is  still  in  its  primitive  stages,  many  phenomena  already 
point  to  ionic  formations  or  electron  effects.  The  silent  electric 
discharge  takes  place  continuously  between  two  conductors 
separated  by  a  dielectric  such  as  glass,  or  gases,  if  the  poten- 
tial difference  of  the  two  conductors  exceeds  a  certain  value. 

In  rarefied  gases  the  discharge  is  accompanied  by  luminous 
appearances  (glow  discharges),  which  are  often  suited  for  in- 
vestigations in  spectrum  analysis;  under  ordinary  pressure 
and  in  daylight  the  gases  do  not  glow;  but  in  the  dark  and  with 
a  sufficiently  high  tension,  even  without  rarefaction,  the  glow 
occurs. 

The  rise  in  temperature  during  the  discharge  is  trifling;  there- 
fore reactions  which  are  brought  about  by  the  latter's  influence 
often  assume  a  different  role  than  those  produced  by  the  in- 
duction spark.  In  the  latter  case  stable  compounds  are  pro- 
duced, which  is  very  natural,  considering  the  high  temperature. 
The  formation  of  labile,  often  endothermic  substances,  is  incited 
by  the  silent  electric  discharge.  These  substances  are  easily 
decomposed  by  stronger  calefaction.  The  great  value  of  these 
reactions  for  simple  syntheses — as  employed  by  nature  in  plants 

261 


262         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

for  producing  the  labile  compounds,  which  serve  as  plant  nourish- 
ment, from  the  most  stable  products  started  with — lies  in  this 
property.  This  problem  is  extremely  important.  The  syn- 
thesis of  substances  important  for  nature — the  carbohydrates, 
albumens — in  the  laboratory  with  our  usual  chemical  resources 
is  only  a  first  step  in  the  realm  of  actual  synthesis.  This  will 
only  be  found  when  we  can  follow  the  paths  which  nature 
herself  chooses  in  preparing  her  products.  Her  methods  are 
undoubtedly  much  simpler  than  the  artificial,  chemical  proc- 
esses that  we  must  make  use  of  in  reaching  the  same  goal. 
The  whole  primary  material  upon  which  we  can  base  the 
formation  of  the  most  various  substances  of  organic  nature  is 
the  atmosphere — are  carbonic  acid,  oxygen,  nitrogen,  and  water. 
The  synthesis  of  complex  substances  from  these  materials 
is  known  to  take  place  under  the  influence  of  light  rays  and  the 
absorption  of  energy.  Such  a  transformation  of  a  system  of 
lower  energy  into  one  of  higher  energy  usually  occurs  only  at 
high  temperatures.  The  silent  electric  discharge  occupies  a 
prominent  place  among  the  forms  of  energy  which,  like  light, 
favor  endothermic  reactions  at  ordinary  temperatures. 

Berthelot,1  in  pointing  to  the  nature  of  the  reactions  occur- 
ring under  its  influence,  which  are  particularly  similar  to  those 
of  plants,  advanced  the  following  views:  In  clear  weather  there 
exists  between  two  strata  of  air  only  one  metre  apart  a  potential 
difference  of  20-30  volts  which,  in  rainy  weather,  can  increase 
to  about  500  volts.  Reactions  can  already  take  place  under 
the  influence  of  such  tensions;  thus  at  7  volts  a  fixation  of  nitro- 
gen by  carbohydrates  can  already  occur;  the  decomposition 
of  carbonic  acid  requires  higher  tensions. 

Opportunities  for  reactions  on  the  surfaces  of  plants,  by 
the  formation  of  potential  differences,  are  likewise  continually 
present.  In  other  words,  Berthelot  ascribes  a  leading  part  in 
natural  syntheses  to  atmospheric  tensions,  which  can  neutralize 
one  another  in  the  form  of  invisible  discharges  (convective  dis- 
charges) through  thin  strata  of  air  acting  like  dielectrics. 

1  Compt.  rend.  131,  772  (1900). 


THE  SILENT  ELECTRIC  DISCHARGE.  263 

Even  if  this  hypothesis  does  not  seem  to  be  scientifically 
well  founded,  it  is  nevertheless  suitable  for  showing  the  im- 
portance of  this  but  little  investigated  domain. 

We  still  know  nothing  of  the  consumption  of  energy  in  the 
reactions  produced  by  the  silent  electric  discharge.  The  spent 
energy  can  be  easily  determined  by  employing  certain  current 
conditions;  it  is  difficult  to  calculate  experimentally  the  utilized 
energy;  this  is  due  to  the  insignificance  of  the  obtained  reac- 
tions and  the  simultaneously  occurring  heat  quantities. 

The  fact  that  Faraday's  law  is  not  applicable  shows  that 
the  reactions  which  are  caused  by  the  discharge  are  not  of  a 
purely  electrochemical  nature.  The  chemical  effect  is  usually 
larger  than  can  be  accounted  for  by  the  minimum  quantities 
of  electricity.  As  shown  by  the  kind  of  reactions,  thermic 
effects  are  also  unlikely,  although  an  influence  of  the  tempera- 
ture produced  by  the  discharge  is  always  manifest.  The  •  suppo- 
sition is  more  probable  that  the  invisible  electric  discharge,  in 
which  cathode  and  ultra-violet  rays  are  present,  introduces  into 
the  system  great  quantities  of  kinetic  energy  by  the  movement 
of  electrons;  this  energy  is  then  transformed  into  chemical 
energy.  This  kinetic  energy  would  then  have  to  be  equivalent 
to  the  heat  of  formation  of  the  occurring  substances,  taking  into 
account  the  part  directly  converted  into  heat.  Bichat  and 
Guntz  1  have  shown  by  a  simple  example,  that  of  ozone,  that 
the  heat  developed  in  the  induction  tube  and  calorimetrically 
measured,  plus  the  heat  of  formation  of  the  produced  ozone, 
is  equal  to  the  calorific  equivalent  of  the  spent  electrical  energy. 

The  actual  efficiency  of  ozonizers  is  extremely  small.  With 
the  best  ozone  apparatus  and  under  the  most  favorable  circum- 
stances only  about  15  per  cent,  of  the  total  energy  can  be 
utilized  for  the  chemical  reaction. 

a.  Arrangements. 

The  well  known  and  variously  shaped  small  ozonizers  of 
Berthelot  and  Siemens  are  generally  satisfactory  for  scientific 

1  Ann.  chim.  phys.  [6]  19,  131  (1890). 


264        ELECTROCHEMISTRY   OF  ORGANIC  COMPOUNDS. 

experiments.  According  to  a  recommendation  of  Losanitsch 
and  Jovitschitsch  the  apparatus  are  suitably  called  "  electrizers." 
The  principle  employed  in  their  construction  is  always  the 
same.  An  air  space  or  chamber,  chosen  as  narrow  as  possible, 
exists  between  two  conductors,  either  metals  or  electrolytes, 
which  are  connected  with  the  terminals  of  an  induction  coiL 


FIG.  9.  FIG.  10. 

The  metals  serving  as  electrodes  are  in  most  cases  separated — 
electrolytes  of  course  always — from  the  discharging  chamber  by 
thin  glass  walls.  Suitable  small  tubes  attached  to  the  appara- 
tus afford  means  of  ingress  and  egress  for  the  gases  or  vapors 
to  be  acted  upon.  The  space  between  the  walls  in  the  dis- 
charging chamber  is  of  great  influence  (A.  de  Hemptinne  J). 

Some  apparatus  used  by  myself  in  experiments  as  yet  un- 
finished may  be  mentioned  here.     The  difference  from  former 
1  Bull,  de  TAcad.  roy.  de  Belg.  [3]  34,  269  (1897). 


THE  SILENT  ELECTRIC  DISCHARGE.  265 

constructions  exists  (in  Fig.  9)  in  the  constant  production  of 
the  vapors  in  a  flask  with  a  ground-glass  neck  made  to  fit  one 
end  of  the  induction  tube;  the  flask  contains  the  reaction  fluid. 
This  apparatus  has  an  arrangement  for  cooling  the  vapors  and 
one  for  working  under  diminished  pressure.  In  Fig.  10  the 
apparatus  can  be  taken  apart  at  the  ground-glass  connection  b 
in  such  a  way  that  liquids,  solids,  and  electrodes  of  various; 
materials,  especially  for  investigating  catalytic  effects,  can 
be  brought  into  it.  The  current  connections  with  the  outer 
coat  is  made  in  Fig.  10  by  means  of  a  platinum  loop  a,  fused 
into  the  side  of  the  tube,  in  which  is  hooked  the  spiral  electrode 
of  any  kind  of  metal  wire. 

Special  attention  in  these  experiments  must  be  paid  to  the 
interrupter  (rheotome l) ;  platinum,  and  mercury  circuit-break- 
ers and  electrolytic  ones  are  applicable.  The  former  pos- 
sesses the  disadvantage  of  great  wear  and  tear,  and  in  prolonged 
experiments  requires  frequent  regulation.  If  kept  clean,  the 
mercury  circuit-breaker  is  very  convenient.  The  Wehnelt 
circuit-breaker  interrupts  high  current  strengths  very  exactly, 
and,  when  suitably  made,  can  be  used  both  with  alternating 
and  direct  currents.  To  save  the  consumption  of  platinum  I 
construct  the  electrolytic  interrupters  by  placing  in  front  of  a 
large  carbon  plate  the  point  of  a  nickel  wire  2  mm.  thick  as 
active  electrode  in  a  2-3%  sodium-hydroxide  solution.  Glass 
worms  regulate  the  temperature  with  high  current  strengths. 
This  simple  and  cheap  arrangement  has  proven  serviceable. 

b.  Chemical  Results. 

The  action  of  the  silent  electric  discharge  upon  organic 
compounds  takes  its  starting  point  in  the  observation  that 
oxygen  under  its  influence  is  polymerized  to  ozone.  Although 
the  work  done  in  this  field,  which  until  recently  was  chiefly 
carried  on  by  the  French  school,  has  not  yet  shown  great  prac- 
tical results,  we  need  not  doubt  that  these  phenomena  deserve 

1  See  also  Leitfaden  des  Rontgenverfahrens,  published  by  Dessauer  and 
Wiesner,  Berlin,  1903. 


266         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

the  greatest  interest  and  are  closely  related,  as  already  em- 
phasized, to  the  fundamental  questions  of  synthesis  in  general. 
Besides  the  experiments  on  the  behavior  of  organic  vapors, 
the  observations  which  have  been  made  on  the  synthesis  of 
simple  organic  compounds  from  carbonic  acid  and  carbon 
monoxide  —  substances  which  we  are  not  accustomed  to  regard 
as  organic  —  are  of  particular  interest.  The  results  so  far  obtained 
are  mentioned  below.  We  are  mostly  indebted  to  Berthelot's 
investigations  along  this  line  of  work. 

/.   Carbonic  Acid  and  Carbon  Monoxide. 

Carbonic  Acid.  —  Berthelot  1  observed  the  decomposition  into 
carbon  monoxide  and  oxygen.  The  reaction  is  reversible,  an 
equilibrium  occurs,  in  which,  however,  the  partially  ozonized 
oxygen  converts  carbon  monoxide  into  carbonic  acid  and  a 
solid  carbon  suboxide,  C^Os,  which  Brodie  2  had  already  formerly 
observed.  Carbon  dioxide,  under  a  pressure  of  3-10  mm. 
mercury,  splits-  up  very  rapidly  and  up  to  70  per  cent,  into 
carbon  monoxide  and  oxygen  (Norman  Collie3). 

Carbonic  acid,  in  the  presence  of  water,  is  converted  into 
formic  acid  and  oxygen  (Losanitsch  and  Jovitschitsch  4)  ;  the 
latter,  partially  ozonized,  produces  hydrogen  peroxide. 

Lob  5  showed  that  moist  carbon  dioxide  also  always  yields 
carbon  monoxide  and  only  the  latter  forms  the  starting  point 
for  formic  acid.  The  following  reactions  occur  : 


2.  CO  +  H20  =  HCOOH, 

3.  302  =  2  03, 
4. 


1  Essai  de  Mecanique  chimique  II,  377  (1879). 

2  London  R.  Soc.  Proceed.  21,  245  (1873);    Lieb.  Ann.  169,  270  (1873). 

3  Journ.  of  the  Chem.  Soc.  465,  1063  (1901). 

*  Ber.  d.  deutsch.  chem.  Gesellsch.  30, 135  (1879). 

8  Sitzungsberichte  d.  niederrheinischen  Gesellschaft  fur  Natur-  u.  Heil- 
kunde  (1903). 


THE   SILENT  ELECTRIC  DISCHARGE.  267 

Carbonic  acid  and  hydrogen,  according  to  the  experiments 
of  Losanitsch  and  Jovitschitsch,1  also  unite  to  form  formic 
acid. 

Carbon  Monoxide.  —  Considering  the  easy  decomposability  of 
carbonic  acid  with  splitting  off  of  carbon  monoxide,  the  latter's 
behavior  is  particularly  interesting.  According  to  Berthelot2 
it  breaks  up  into  carbonic  acid  and  the  above-mentioned  sub- 
oxide  : 

C02+C403. 


Moist  carbon  monoxide,  according  to  the  concordant  results 
of  Losanitsch  1  and  Jovitschitsch,  of  Lob  3,  and  of  Hemptinne,4 
yields  formic  acid.  There  are  also  always  formed  some  car- 
bonic acid  (Maquenne,5  and  Hemptinne)  and  hydrogen  (Ma- 
quenne).  The  dimensions  of  the  "'electrizer,"  particularly 
the  distance  of  the  walls  between  which  the  discharge  occurs, 
are  of  special  influence  on  the  result  (Hemptinne). 

The  influence  of  the  experimental  conditions  is  shown  in 
the  action  of  the  silent  discharge  upon  a  mixture  of  carbon 
monoxide  and  hydrogen.  Thenard,  Brodie,  and  Berthelot  6 
found  a  solid  body  (C4H303)n;  Berthelot  also  observed  a  little 
carbon  dioxide,  acetylene,  and  an  olefine-like  hydrocarbon. 
Losanitsch  and  Jovitschitsch  7  obtained  formaldehyde  and 
its  polymers;  Hemptinne  observed  an  oily  liquid,  without 
being  able  to  say  anything  definite  regarding  the  formation 
of  formaldehyde. 

At  any  rate  all  these  experiments  are  worthy  of  the  most 
thorough  study.  If  the  assertion  of  Phipson  8  is  correct,  that 
in  plants  hydrogen  peroxide  first  produces  formaldehyde  from 
the  carbonic  acid  (C02  +  H202  =  CH20  +  03),  the  possibility  of 


M.  c. 

2  Essai  de  Mecanique  chimique  IT,  379  (1879). 

3  See  note  5  on  page  266. 

*  Bull,  de  1'Acad.  roy.  de  Belg   [3]  34,  269  (1897). 

5  Bull.  soc.  chim.  [2]"  39,  308  (1883). 

6  Essai  de  Me'canique  chimique  II,  382  (1879). 
71.  c. 

8  Chem.  News,  50,  37,  288  (1884). 


268         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

.the  formation  of  sugar  by  polymerization  is  at  once  given.  The 
well-known  Bayer  theory,  of  the  formation  of  sugar  in  plants, 
in  connection  with  the  above-mentioned  view  of  Berthelot  on 
the  importance  of  atmospheric  tensions  for  the  chemical  re- 
actions of  plants  thus  obtains  new  essential,  and  experimentally 
accessible,  facts. 

Recent  investigations  of  Berthelot  1  deserve  the  greatest 
attention  exactly  in  this  connection.  He  found: 

1.  Carbon  monoxide  and  carbon  dioxide  condense  with  an 
excess  of  hydrogen  to  carbohydrates: 

n(CO  +  H2)=C«H2nOn; 

n(C02  +  2H2)  =  CnH2nOn  +  nH20. 

2.  If  only  a    little   hydrogen  is  present,  complicated  com- 
pounds rich  in  oxygen  result. 

3.  In  a  mixture  of  carbon  monoxide,  carbon  dioxide,  hydro- 
gen, and  nitrogen,  the  discharge  produces  nitrogen  containing 
compounds  having  the  formula  : 

(COH3Njn,     or     (COH3N)n  +  nH20, 

which   are   comparable  with  hydrocyanic  acid,  and   the  com- 
pounds of  the  carbamide  and  xanthine  groups. 

With  an  excess  of  carbon  monoxide  Berthelot  finds  sub- 
stances which  seem  related  to  parabanic  acid.  If  water  occurs 
in  the  reactions,  ammonium  nitrite  is  present. 

Berthelot's  observations  are  confirmed  by  the  experiments  of 
A.  Slosse,2  who,  by  subjecting  a  mixture  of  1  volume  carbon 
monoxide  and  2  volumes  hydrogen  to  the  induction  action  in  an 
ozonizer,  obtained  a  crystalline,  fermentable  sugar  which  could 
have  been  formed  from  formaldehyde  and  methyl  alcohol— 
both  of  which  can  be  shown  to  be  present  —  by  the  further 
action  of  the  discharge: 

=  CH20; 


1  Compt.  rend.  126,  609  (1898). 

2  Bull,  de  1'Acad.  roy.  de  Belg.  35,  547  (1898). 


THE  SILENT  ELECTRIC  DISCHARGE.  269 

Bert  helot  has  published  a  paper  1  on  the  apparatus  em- 
ployed in  his  experiments,  the  methods  of  the  quantitative 
determinations,  the  influence  of  the  conditions  on  the  reaction 
velocity,  and  the  dependence  of  the  results  upon  the  duration 
of  the  experiment.  The  latter  is  particularly  important  for 
the  theoretical  interpretation  of  the  results.  Simple,  binary 
compounds  are  primarily  formed  which  are  secondarily  poly- 
merized to  complex  compounds  —  similarly  as  in  physiological 
processes,  in  which  the  assimilated  substances,  after  being 
split  up  into  simpler  substances  for  the  purpose  of  nutrition, 
are  again  united  to  complicated  compounds.2 

Losanitsch  and  Jovitschitsch,3  by  the  action  of  the  silent 
electric  discharge  upon  a  mixture  of  carbon  monoxide  with 
other  gases,  have  also  accomplished  the  following  syntheses. 
They  obtained: 

1.  From  carbon  monoxide  and  hydrogen  sulphide  :  Formalde- 
hyde and  sulphur,  and  thioformaldehyde  and  its  polymers 
respectively,  besides  water, 


HCOH  +  H2S  =  HCSH  +  H20. 

2.  From  carbon  monoxide  and  hydrochloric  acid:   The  un- 
stable f  ormylchloride  : 

=  HCOC1. 


3.  From  carbon  disulphide  and  hydrogen  :  Hydrogen  sulphide 
and  carbon  monosulphide  : 


4.  From  hydrogen  sulphide  and  carbon  monoxide:  Carbon 
oxysulphide  and  carbon  monosulphide: 


1  Compt.  rend.  126,  561  (1898);  131,  772  (1900). 

21.  c. 

3  Ber.  d.  deutsch.  chem.  Gesellsch.  30,  135  (1897). 


270         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 
5.  From  carbon  monoxide  and  ammonia:  Formamide: 

=  HCONH2. 


According  to  Slosse,1  1  vol.  CO  and  2  vols.  NH3  give  a 
crystalline  substance  resembling  urea. 

6.  From  nitrogen  and  water:  Ammonium  nitrite: 

N2  +  2  H20  =  NH4-N02. 

In  the  further  description  of  the  results  obtained  in  the 
realm  of  silent  discharges  we  will  first  consider  the  behavior  of 
single  organic  substances,  then  that  of  mixtures. 

//.  Hydrocarbons. 

Methane.  —  Aliphatic  hydrocarbons,  exposed  to  the  action 
of  a  high-tension  discharge,  yield  hydrogen,  a  little  acetylene, 
which  in  the  course  of  the  experiment  can  again  disappear  by 
polymerization,  and  polymerized  hydrocarbons.  From  methane 
Berthelot  2  obtained  the  last-mentioned  gases,  a  resinous  hydro- 
carbon, and  traces  of  a  fluid  possessing  a  turpentine  odor.  He 
found  —  in  percentages  by  volume  —  from  100  CH4:  105.2  H2, 
4.4  CH4,  a  solid  hydrocarbon  of  the  empirical  formula  Ci0Hi8. 

Methane  and  oxygen,  according  to  Maquenne,3  yield  formal- 
dehyde besides  considerable  formic  acid. 

Methane  and  carbon  monoxide,  according  to  Losanitsch  and 
Jovitschitsch,4  unite  to  acetaldehyde  and  its  condensation  and 
polymerization  products;  according  to  Hemptinne,5  aldehydic 
substances. 

Methane  and  carbonic  acid  condense  (Thenard  and  Berthe- 
lot 2)  to  an  insoluble  carbohydrate  ;  Berthelot  observed  the 
presence  of  a  trace  of  butyric  acid.  The  residual  gases  con- 
tained a  little  acetylene  and  considerable  carbon  monoxide. 

1  Bull,  de  1'Acad.  roy.  de  Belg.  35,  547  (1898). 

2Compt.   rend.   82,    1360    (1876);     Traite  de    Mecanique    Chimique  II, 
379  (1879).     See  also  Compt.  rend.  126,  561  (1898). 
8  Bull.  soc.  chim.  37,  298  (1882). 
4  Ber.  d.  deutsch.  chem.  Gesellsch.  30,  135  (1897). 
6  Bull,  de  PAcad.  roy.  de  Belg.  [3]  34,  275  (1897). 


THE  SILENT  ELECTRIC  DISCHARGE.  271 

Methane  and  nitrogen  in  the  mixture  100  CH4  +  100  N2  give 
117.7  H2,  3.4  CH4,  74  N2,  and  a  solid  body  having  approxi- 
mately the  composition,  CgHi2N4  (Berthelot  J). 

Ethane.  —  From  pure  ethane  Berthelot,  at  the  beginning 
of  the  experiment,  obtained  (1.  c.)  a  little  acetylene  and  ethylene 
besides  a  resinous  hydrocarbon.  He  found  at  the  end  of  the 
experiment,  from  100  C2H4.  107.8  H2,  0.7  CH4,  Ci0Hi8.  The 
unsaturated  hydrocarbons  had  become  polymerized. 

Ethane  and  carbon  monoxide  yielded  Hemptinne  (1.  c.)  chiefly 
acetaldehyde,  also  some  acetone: 

CH3  •  CH3  +  CO  =  CH3  •  CO  •  CH3. 

Ethane  and  nitrogen.  —  There  were  obtained  from  100  C2H6  + 
100  N2  (Berthelot):  9S.2  H2,  3.0  CH4,  73.5  N2,  Ci6H32N4. 

Ethylene.—  100  C2H4  gave  25.15  H2,  4.35  C2H6  (C8H14)n 
(Berthelot).  In  former  experiments  Berthelot  had  obtained  a 
fluid  (C2oHi6.6)  already  observed  by  Thenard. 

Ethylene  and  nitrogen.—  100  C2H4  +  100  N2  gave  28.6  H2, 
0.4  C2H6,  62.2  N2,  Ci6H32N4. 

Propylene.—  100  parts  yielded:  34.2  H2,  0.7  CH4,  Ci5H26. 

Propykne  and  nitrogen.  —  100  C3H6  +  100  N2  gave  17.8  H2, 
60.5  N2,  Ci5H28N4. 

Trimethylene.—  100  C3H6  -^37.31^,  1.4  CH4,  Ci5H26. 

Trimethylene  and  nitrogen.  —  100  C3H6  +  100  N2->41.4H2, 
1.6  CH4,  61.4  N2,  Ci5H26N4. 

Acetylene.—  100  C2H2  ->  1.8  H2,  0.8  C2  H4,  0.08  C2H6,  and  an 
explosive  substance.  In  the  presence  of  hydrogen  this  sub- 
stance is  partially  absorbed  by  the  acetylene. 

Acetylene  and  nitrogen.  —  100  C2H2  +  100N2  gave  no  hydro- 
gen and  no  hydrocarbon,  but  88.6  N2  and  a  solid  substance, 
Ci6H16N2. 

Allylene.—  100  C3H4-*3  H2,  (Ci5Hi9)2. 

Allylene   and   nitrogen.  —  100  C3H4  +  100    H2  ->  82.2   N2, 


In  the  experiments  of  Berthelot  the  gas  analyses  refer  to 
the  residual  gas  volume  after  the  discharge  has  acted  on  the 
1  Compt.  rend.  126,  567  (1898). 


272         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

gaseous  mixture  for  24  hours.  The  high  molecular  formulae 
give  approximately  the  composition  of  the  solid  condensation 
products. 

Berthelot l  thus  summarizes  his  experiences  as  to  these 
reactions : 

1.  The  limit  hydrocarbons  Cn~H.2n+2  lose  2  atoms  of  hydrogen 
per  molecule.     Solid  hydrocarbons,  most  probably  of  a  cyclical 
nature,  are  formed  as  polymerization  products. 

2.  The  olefines  CnH2n  also  polymerize  with  loss  of  hydrogen. 
The  solid  products  hereby  formed,    (CnH-2n)m  —  H2,  in  which 
ra  equals  4  or  5,  or  a  multiple  of  these  values,  remind  one  of 
the    camphenes,   so    far  as    their    composition    is    concerned. 
They  certainly  belong  to  the  cyclical  hydrocarbons. 

3.  The  acetylene  hydrocarbons,  CnH-2^-2,  polymerize  without 
loss  of  hydrogen. 

4.  All  hydrocarbons  take  up  nitrogen,   forming  probably 
cyclical  polyamines;  methane  and  ethylene  hydrocarbons  seem 
to  give  tetramines;  and  acetylene  hydrocarbons,  diamines. 

Benzene  gave  Hemptinne 2  resinous  substances,  several 
hydrocarbons,  a  little  acetylene,  and  hydrogen. 

Benzene  and  hydrogen  easily  unite  under  the  influence  of 
the  discharge.  Berthelot 3  found  that  1  cc.  benzene  takes 
up  250  cc.  hydrogen,  i.e.,  about  2  equivalents,  forming  a 
solid  polymeric  hydrocarbon  (C6H8)n. 

Benzene  and  nitrogen-,,  according  to  Berthelot,4  form  a 
polymeric  condensation  product,  one  part  by  weight  of  ben- 
zene taking  up  about  0.12  part  by  weight  of  nitrogen.  The 
substance,  on  being  heated,  splits  off  ammonia  and  seems  to 
be  a  diphenylenediamine.  Recently  Berthelot  5  has  found  that 
argon  is  also  absorbed  by  aromatic  compounds,  especially  by 
mercury  phenide,  forming  a  mercurargon  phenide.  Mercury 
methide,  on  the  contrary,  does  not  absorb  argon,  but  if  nitrogen 

1  See  also  Jahrb.  d.  Elektrochemie  of  Nernst  and  Borchers,  V,  202  et  seq. 
(1899). 

2  Ztschr.  f.  phys.  Chemie  25,  298  (1898) 

3  Compt.  rend.  82,  1360  (1876). 

4  Ann.  chim.  phys.  11,  35  (1897). 

5  Compt.  rend.  129,  71,  378  (1899). 


THE  SILENT  ELECTRIC  DISCHARGE. 


273 


is  simultaneously  present,  it  condenses  with  this  to  a  con- 
densation product  of  approximately  the  formula  C2oH34N5. 

Turpentine  (C2oHi6)  unites  with  about  2.5  equivalents  of 
hydrogen  to  a  solid  polymeric  body.1 

///.  Alcohols. 

Methyl  Alcohol. — According  to  Maquenne,2  the  vapor  of 
methyl  alcohol  is  decomposed  by  the  silent  discharge  chiefly 
into  methane  and  carbon  monoxide;  some  hydrogen,  ethylene, 
and  acetylene  and  very  little  carbonic  acid,  are  also  produced. 
The  quantity  of  hydrogen  increases  with  increasing  pressure 
(from  3-100  mm.  mercury  pressure),  that  of  the  other  products 
decreases: 


Pressure. 

3  mm. 

100  mm. 

CO 

24.3 

19.6 

CO2     

0.0 

0.0 

CA+CA  

4.3 
51.0 

0.9 

36.7 

H2  ':::.'.'.'.'.'.'.'.::: 

20.4 

42.8 

A  decomposition  is  caused  by  a  high  temperature  similar  to 
that  produced  by  the  discharge. 

A.  Hemptinne  subjected  a  large  number  of  substances  to 
rapid  electric  oscillations  in  an  arrangement  which,  according 
to  the  method  of  Lecher,3  permitted  an  investigation  of  the 
influence  of  various  wave  lengths.4  He  found  that  methyl 
alcohol  5  at  15  mm.  pressure  and  with  weak  oscillations  gave : 

Undecomposed  alcohol 2.0% 

Carbonic  acid 4.2% 

Carbon  monoxide 30.4% 

Hydrogen 30.5% 

Methane  (and  other  hydrocarbons).  .  .  32.9% 

1  Trait  e  de  Mecanique  chimique  IT,  382  (1879). 

8  Bull.  soc.  chim.  [2] 37, 298  (1882);  40,  60  (1883). 

«  Wied.  Ann.  41,  850  (1890). 

4  Ztschr.  f .  phys.  Chem,  22,  358  (1897). 

8  Ibid.  25,  284  (1898). 


274         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Stronger  oscillations  produced  about  the  same  effects. 
Hemptinne  suggests  the  following  three  problematical  equa- 
tions for  explaining  the  reaction: 


the  oxygen  acts  in  turn  upon  the  methane  and  forms  C02,  CO, 
and  H20,  while  methane  itself  simultaneously  breaks  up  into 
hydrogen  and  other  hydrocarbons. 

The  following  processes  seem  to  him  less  likely: 

II.  CH3OH  =  CO  +  2H2, 

because  the  solid  reaction  product  of  hydrogen  and  carbon 
monoxide,  which  Berthelot  found,  is  not  present,  and: 

III. 

with  subsequent  polymerization,  since  here  the  formation  of 
large  quantities  of  methane  is  difficult  to  explain. 

Owing  to  the  present  existing  difficulty  of  explaining  the 
complex  action  of  electric  oscillations,  I  should  like  to  here 
refer,  but  only  by  way  of  suggestion,  to  a  further  possibility 
which  takes  account  of  the  polymerizing  influence  of  the  oscil- 
lations. It  is  imaginable  that  primarily  two  or  several  mole- 
cules of  methyl  alcohol  become  associated  and  yield  a  product 
which  is  broken  up  during  the  progress  of  the  experiment. 
The  decomposition  products  thus  formed  are  then  further 
effected  by  the  influence  of  the  oscillations.  The  total  equation 
would  then  be  the  following  : 

2CH3  OH  •=  CH4  +  CO  +  H2  +  H20. 

As  some  carbon  dioxide  is  always  formed  from  carbon 
monoxide  and  water,  such  a  breaking  up  of  the  molecules  would 
agree  with  the  analytical  results  of  Hemptinne. 

Ethyl  Alcohol.  —  Maquenne  l  obtained  a  gas  which  possessed 

1  Bull.  soc.  chim.  [2]  37,  298  (1882);  40,  61  (1883). 


THE  SILENT  ELECTRIC  DISCHARGE. 


275 


a  strong  aldehydic  odor,  and  contained  hydrogen,  ethane,  ethy- 
lene,  acetylene,  carbon  monoxide,  and  carbon  dioxide.  He 
determined  the  following  results  for  various  pressures: 


Pressure. 

2  mm. 

110  mm. 

CO2.  . 

2.2 

0  0 

CO 

11  0 

) 

CH,C2H,... 

14.0 
30  1 

|      14.8 
19  8 

rf2    . 

42  6 

65  4 

Hemptinne  1  found : 

Undecomposed  alcohol 3% 

Carbon  dioxide 2% 

"      monoxide , 22% 

Hydrogen 25% 

Ethane  and  methane 48% 

To  prove  the  supposition  of  a  decomposition:  C2 
=  C2H6  +  0,  Hemptinne  added  some  phosphorus  to  the  vapors, 
for  immediately  binding  the  oxygen  occurring  intermediately. 
He  actually  found  a  decrease  in  carbon  monoxide  and  the 
hydrocarbons  and  a  considerable  increase  in  the  quantity  of 
hydrogen.  Carbon  dioxide  was  not  present.  On  the  con- 
trary, if  oxygen  is  added  directly  to  the  alcohol  vapor,  the 
quantities  of  carbon  mon-  and  dioxide  and  of  the  hydrocarbons 
increase  considerably,  while  the  quantity  of  hydrogen  decreases. 
These  phenomena,  of  course,  do  not  prove,  the  primary  process, 
C2H5OH  =  C2H6  +  0,  which  is  altogether  unlikely.  For  the  chief 
change  occurs  in  the  proportion  of  hydrogen  to  hydrocarbon 
(without  P:  20%  H2,  62.5%  C2H6  +  CH4;  with  P:  65%  H2, 
27%  C2H6  +  CH4);  it  points  to  the  influence  of  the  medium 
upon  the  reaction  velocity  and  the  equilibrium,  but  does  not 
permit  a  decision  as  to  the  course  of  the  reaction.  The  explana- 
tion of  these  processes  occurring  with  simple  substances  still 
requires  a  great  deal  of  experimental  work. 


1.  c. 


276         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Absolute,  fluid  alcohol,  according  to  Bert  helot,1  breaks  up 
slowly  with  evolution  of  hydrogen  and  ethane.  Aldehyde  is 
simultaneously  produced  and  a  complex  hydrocarbon  having 
perhaps  the  composition  CnH2n. 

Hemptinne  2  also  investigated  the  following  alcohols : 

Propyl  Alcohol. — Result : 

Undecomposed  alcohol 2% 

Carbon  monoxide 16% 

Hydrogen.  .  ., 37% 

Propane,  ethane,  and  methane 45% 

Isopropyl  Alcohol  breaks  up,  under  similar  conditions,  in 
almost  exactly  the  same  way  as  the  normal  alcohol. 

Allyl  Alcohol  was  exposed  for  only  a  minute  to  electric  oscil- 
lations; it  yielded: 

Undecomposed  alcohol 35% 

Hydrocarbons,  CnH2n 35% 

Carbon  monoxide 10% 

Hydrogen,  and  other  hydrocarbons.  . .  .   20% 

Glycerin. — The  gaseous  products  formed  are  carbon  dioxide, 
carbon  monoxide,  and  hydrogen. 

Glycol  gives  carbon  dioxide,  carbon  monoxide,  hydrogen, 
and  methane. 

Phenol  is  decomposed,  splitting  off  a  gasc  omposed  of  car- 
bon mon-  and  dioxide  and  hydrogen. 

4 

IV.  Aldehydes  and  Ketones. 

Aldehydes  and  ketones  were  also  investigated  by  Hemp- 
tinne.2 

Acetaldehyde  gives  carbon  monoxide,  hydrogen,  and  methane. 
Paraldehyde. — The  gaseous  products  formed  are  carbonic  acid, 

1  Compt.  rend.  126,  693  (1898).  2 1.  c. 


THE  SILENT   ELECTRIC  DISCHARGE. 


277 


hydrocarbons  (CnH2n),  carbon  monoxide;  hydrogen,  and  meth- 
ane. 

Propylaldehyde  breaks  up  in  a  different  manner  than  the 
isomeric  allyl  alcohol.  The  gas,  separated  from  the  aldehyde, 
contained  carbonic  acid,  methane,  and  ethane,  hydrocarbons, 
CnH2n,  carbon  monoxide,  and  hydrogen. 

Acetone,  likewise  isomeric  with  allyl  alcohol,  gives  the  same 
products  as  propyl  aldehyde.  As  the  quantity  of  carbon  mon- 
oxide does  not  decrease  in  the  presence  of  phosphorus,  Hemp- 
tinne  concludes  that  the  following  decomposition  process  occurs: 

CH3COCH3  =  C2H6+CO. 

According  to  Maquenne  l  acetone  vapor  is  decomposed  by 
the  electric  discharge  into  hydrogen,  ethane,  and  carbon  mon- 
oxide, a  small  quantity  of  acetylene  and  carbon  dioxide  being 
also  formed.  The  quantity  ratios  are  less  dependent  upon  the 
pressure  than  in  the  case  of  methyl  and  ethyl  alcohol: 


Pressure. 

Trifling. 

100  mm. 

CO,  . 

1.1 

0.6 

CO  

37  .  5 

42.1 

C2H4. 

4.3 

2.9 

CH  .. 

32.4 

30.0 

H2 

24  7 

24  4 

Glyoxal  breaks  up  into  carbonic  acid,  hydrocarbons  (CnH2n), 
and  hydrogen. 

V.  Acids  and  Esters. 

Formic  Acid. — Maquenne 2  has  investigated  the  action  of 
the  discharge  upon  formic-acid  vapor  under  various  pressures. 
He  found  carbon  monoxide,  carbonic  acid,  and  hydrogen.  With 
increasing  pressure  (2-100  mm.  mercury)  the  quantity  of 
carbon  monoxide  decreases,  while  the  quantities  of  carbonic 


1  Bull.  soc.  chim.  [2]  40,  63  (1883). 

2  Ibid.  39,  306  (1883). 


278         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

acid  and  hydrogen  increase  correspondingly.     Hemptinne  1  ob- 
tained similar  results. 

Formic  Methyl  Ester  yielded  the  following  gases  (Maquenne  2)  : 

Carbon  dioxide  ....................  8.1% 

monoxide  ..................  46.8%  , 

Ethylene.  ..  .......................  0.5% 

Methane  ..........................  20.6% 

Hydrogen  .........................  24.0% 

Formic  Ethyl  Ester  gives  (Hemptinne): 

Carbon  dioxide  ....................  -  13% 

fc       monoxide  ..................  42% 

Hydrogen  .........................  25% 

Ethane  and  methane  ................  20% 

Acetic  Acid.—  Besides  hydrogen,  carbon  mon-  and  dioxides, 
Maquenne  3  also  obtained  methane,  ethylene,  and  acetylene. 
With  increasing  pressure  he  found  an  increase  in  hydrogen  and 
carbon  monoxide,  a  decrease  in  carbonic  acid  and  hydrocarbons. 
Hemptinne  observed  similar  results  with  his  experimental 
arrangement.  He  accepts  the  following  as  the  primary  decom- 
position process,  corresponding  to  that  of  the  alcohols: 


Hemptinne  does  this  to  explain  the  presence  of  large  quantities 
of  ethylene. 

Acetic  Methyl  Ester,  according  to  Hemptinne,  breaks  up 
quantitatively  almost  in  the  same  manner  as  the  isomeric  formic 
ethyl  ester  : 

Carbon  dioxide  ......................  11% 

"       monoxide  ....................  47% 

Hydrogen  ..........................  20% 

Ethane  and  methane  .................  22% 

M.  c. 

2  Bull.   soc.  chim.   [2]  40,  64  (1883). 
»  Ibid.  39,  306  (1883). 


THE  SILENT  ELECTRIC  DISCHARGE.  279 

Propionic  Acid  gives  carbonic  acid,  hydrocarbons  (CnH2n), 
carbon  monoxide,  hydrogen,  and  saturated  hydrocarbons. 

Glyceric  Acid. — Although  glycerin  did  not  yield  any  hydro- 
carbons, there  were  obtained,  on  using  glyceric  acid,  besides 
carbon  mon-  and  dioxides  and  hydrogen,  about  20%  methane. 

Glycollic  Acid.— This  acid,  CH2OHCOOH,  breaks  up  smoothly 
into  hydrogen  (70%)  and  carbonic  acid  (30%). 

Oxalic  Acid  splits  off  carbonic  acid,  carbon  monoxide,  and 
hydrogen. 

Benzoic  Acid  gives  the  same  products.  Hemptinne,  who 
has  investigated  the  last-mentioned  acids,  draws  the  conclusion 
from  his  observations  that  the  molecule  is  burst  by  the  influence 
of  the  electric  vibrations,  whereby  isomeric  substances  often 
give  the  same  bodies,  and  sometimes  various  decomposition 
products. 

VI.  Concerning  the  Binding  of  Nitrogen  to  Organic  Substances. 

(Berthelot's  Investigations.) 
Alcohols  and  Nitrogen.1 

Berthelot  subjected  weighed  quantities  of  the  alcohols  and 
certain  volumes  of  nitrogen  to  the  action  of  the  silent  electric 
discharge.  In  most  cases  the  action  was  limited  to  24  hours 
(when  it  was  continued  for  a  longer  period,  an  absorption 
of  nitrogen  no  longer  occurred).  He  obtained  the  following 
results 

Methyl  Alcohol.  —  0.0515  g.  and  11.5  cc.  N2  were  used. 
Composition  of  the  resulting  gas:  H2=18.5  cc.,  CO  =  0.9  cc., 
absorbed  nitrogen:  9.4  cc. 

These  values  correspond  to  the  process: 

CH3OH+iN-H; 

a  body  of  the  composition  C4H12N204  or  [C2H(OH)NH2  +  H20]2 
must  therefore  have  been  formed.  This  formula  points  to  the 
formation  of  an  amidine  or  its  hydrate. 

1  Compt.  rend.  126,  616  (1898). 


280         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

The  alcohol  is  also  decomposed  by  itself,  which  could  be 
proved  by  experiments  of  short  duration  in  which  no  notable 
absorption  of  nitrogen  had  taken  place.  According  to  the  gas 
analyses,  the  decomposition  of  the  alcohol  occurs  as  shown 
in  the  equations: 

2CH3OH  =  CH4  +  C02  +  2H2, 


CH3OH  =  CO  +  2H2. 

(Cf.  the  experiments  of  Hemptinne,  p.  274.) 

The  other  alcohols  behave  analogously. 

Ethyl  Alcohol.  —  There  were  employed  0.056  g.  and  19.1  cc. 
N2.  Gas  obtained:  H2  =  26.8  cc.,  C02  =  0.2  cc.,  N2  =  8.2  cc.; 
absorbed  nitrogen,  10.9  cc. 

These  values  represent  the  reaction 

C2H5OH-H2+0.8N, 

from  which  (taking  into  consideration  the  alcohol  decomposed 
without  absorption  of  nitrogen)  the  formation  of  an  amidine 
of  the  formula 

C4H8N202  =  [C2H(OH)NH2]2 

results. 

Normal  Propyl  Alcohol.  —  Employed  0.082  g.  and  19.6  cc. 
nitrogen.  Gas  obtained:  H2  =  23.4  cc.,  C02  =  2.0  cc., 
CO  =  0.2  cc.,  N2  =  7.4  cc.;  absorbed  nitrogen,  12.2  cc. 

Process:  C3H7OH-H2  +  N, 
from  which  the  formation  of  the  amidine, 

[C3H2(NH2)H20]2    or    [C3H3(OH)NH2]2, 

is  inferred. 

Isopropyl  Alcohol  shows  the  same  ratios  as  the  normal 
alcohol. 


THE  SILENT  ELECTRIC  DISCHARGE.  281 

Allyl  Alcohol.—  Employed:  0.150  g.  and  23.5  cc.  N2. 
Residual  gas:  H2  =  6.8  cc.;  N2  =  4.3  cc.  Absorbed  nitrogen, 
19.2  cc. 

Process:    3C3H5OH  +  N2  -  f  H, 
from  which  is  inferred  the  formation  of  the  amidine, 


Phenol  and  pyrocatechin  readily  absorb  nitrogen  ;  pyrogallol, 
hydroquinone,  and  resorcin  absorb  the  gas  quite  slowly. 

Ethers  and  Nitrogen.1 

Ethylene  Oxide.—  100  cc.  C2H40  and  115.5  cc.  N2  give: 
H2  =  5.5  cc.,  C2H6  =  0.4cc.,  N2  =  10.1  cc.  Absorbed  nitrogen. 
105.9  c.c.  The  formation  of  a  body, 


is  inferred;  it  could  be  considered  as  an  isomer  of  a  hydrate 
of  cyanamide. 

Methyl  Ether.—  100  cc.  (CH3)20  and  127.9  cc.  N2  give:: 
H2  =  86  cc.,  N2  =  65.6  cc.  Absorbed  nitrogen:  62.3  cc. 

The  ratio  of  the  elements  which  react  is  the  following: 

(CH3)20-1.72H  +  1.25N. 

The  proportions  are  similar  to  those  of  the  isomeric  ethyl  alco- 
hol, but  in  the  case  of  methyl  ether  they  indicate  a  mixture. 

Ethyl  Ether.—  100  cc.  (C2H5)0  and  141  cc.  N2  give: 
H2  =  174.2  cc.,  N2  =  44.6  cc.  Absorbed  nitrogen  :  96.4  cc. 

Ratio  of  the  reacting  elements  : 

(C2H5)0-3.58H  +  N2. 

Ethyl  ether  therefore  gives  off  twice  as  much  hydrogen  and 
absorbs  twice  as  much  nitrogen  as  methyl  ether,  which  seems 
to  point  to  a  fixed  ratio  between  the  nitrogen  compounds  formed 
and  the  molecular  weight  of  the  compounds  started  with. 


282         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Aldehydes,  Ketones,  and  Nitrogen.1 

Acetaldehyde.— Employed:  24  cc.  CH3CHO  and  22.8  cc.  N2. 
Based  on  100  cc.  aldehyde,  there  were  obtained  at  the  end 
of  the  reaction:  H2  =  25.8  cc.,  H2  =  59.6  cc.  Absorbed  nitro- 
gen: 35.4  cc. 

The  ratio  of  the  reacting  elements  is  expressed  by  the 
formula 

C2-H3.50No.35. 

The  ratio  also  remains  constant  with  an  excess  of  nitrogen, 
and  leads  to  the  reaction  product 

Ci0H18N205, 

which,  judging  from  its  marked  basic  character,  seems  to  con- 
tain amido-groups. 

Ethylene  oxide,  isomeric  with  this  aldehyde,  combines  with 
five  times  as  much  nitrogen. 

Propyl  Aldehyde. — A  large  excess  of'  nitrogen  being  present, 
there  were  formed,  based  on  100  cc.  C2H5CHO  vapor:  H2  = 
43.6  cc.,  C02+ CO  =  4  cc.  Absorbed  nitrogen:  66.7  cc. 

These  quantities  correspond  to  a  product  CgHieN^s,  in 
which  there  are  likewise  supposed  to  be  several  amido-groups. 

Acetone. — By  employing  an  excess  of  nitrogen,  there  were 
formed,  based  upon  100  8C.  CH3COCH3  vapor:  H2  =  33.3  cc. 
Absorbed  nitrogen:  89  cc. 

These  relations  are  expressed  by  the  formula 

[C3H(OH)(NH2)2]n. 

Allyl  alcohol,  which  is  isomeric  with  acetone,  absorbs  only 
one  third  as  much  nitrogen  as  acetone  takes  up  and  only  half 
that  taken  up  by  propyl  aldehyde. 

Methylal. — With  an  excess  of  nitrogen  there  are  formed 
from  100  cc.  CH2(OCH3)2:  H2  =  71.1  cc.,  C02  =  4.4  cc., 
CO  =  2.2  cc.  Absorbed  nitrogen:  128.9  cc. 

1  Compt.  rend.  120,  071  (1898). 


THE  SILENT  ELECTRIC  DISCHARGE.  28$ 

Berthelot  seems  to  refer  the  calculated  composition  of  the 
reduction  product 

C9H8N8,    6H20 

to  polyamines  having  many  hydroxyl  groups  and  derived  from 
the  type  (CHN)n,  i.e.,  bodies  which  were  obtained  by  him  from 
carbon  monoxide,  hydrogen,  and  nitrogen  by  means  of  the 
silent  electric  discharge. 

The  following  experiments  could  not  be  carried  out  to  the 
end  of  the  reaction  on  account  of  the  trifling  vapor  tension  of 
the  materials  started  with. 

Aldol  takes  up  large  quantities  of  nitrogen,  giving  off  trifling 
amounts  of  hydrogen;  paraldehyde  behaves  similarly.  Trioxy- 
methylene,  on  the  contrary,  and  formaldehyde  solution  absorb 
nitrogen  only  very  slowly. 

Camphor  takes  up  nitrogen,  forming  a  basic  body. 

Benzaldehyde,  benzoin,  cinnamic  aldehyde,  salicylic  aldehyde, 
furfurol,  and  qvLnone,  under  the  influence  of  the  discharge, 
absorb  nitrogen  more  or  less  rapidly. 

Glucose,  cellulose  (paper),  and  dextrine1  can  slowly  take  up 
nitrogen;  likewise  the  humus  substances  obtained  by  the  action 
of  concentrated  hydrochloric  acid  upon  sugar. 

Acids  and  Nitrogen.2 

Formic  Acid.— Since  formic  acid  is  easily  split  up  by  the  silent 
electric  discharge  into  carbon  mon-  and  dioxides  and  hydrogen,, 
a  noticeable  absorption  of  nitrogen  does  not  occur,  but  formic 
methyl  ester,  although  being  likewise  fundamentally  broken 
up,  takes  up  larger  quantities  of  nitrogen. 

Acetic  Acid. — This  acid  absorbs  nitrogen,  forming  trifling 
quantities  of  ammonia  and  a  product  which,  according  to  the 
analyses  of  the  gases  obtained  by  the  discharge,  is  said  to  have 
the  composition  of  an  amine  or  amide  (Berthelot).  The  be- 
havior of  acetic  methyl  ester  gives  results  which  call  to  mind 

1  Essai  de  Mecanique  chimique  II,  388  (1879). 
2Compt.  rend.  126,  681  (1898). 


ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

those  of  acetic  acid  and  methyl  alcohol  when  each  substance 
is  subjected  by  itself  to  reaction  with  nitrogen. 

Other  acids  investigated  were: 

Propionic  acid,  crotonic  acid,  benzoic  acid,  succinic  acid, 
male'ic  and  fumaric  acid,  phthalic  acid,  camphoric  acid,  gly collie 
acid,  lactic  acid,  malic  acid,  tartaric  acid,  the  oxybenzoic  acids, 
pyroracemic  acid,  laevulinic  acid,  dehydracetic  acid,  and  aceto- 
acetic  acid  (or  its  esters). 

All  these  substances  (with  the  exception  of  fumaric  and 
phthalic  acid,  which,  under  the  experimental  conditions,  do 
not  absorb  nitrogen)  take  up  more  or  less  readily  varying 
quantities  of  nitrogen.  The  m-oxybenzoic  acid  absorbs  con- 
siderably less  easily  than  its  isomers. 

Nitrogen  Compounds  and  Nitrogen.1 

Methylamine.  —  Hydrogen  and  nitrogen  are  split  off,  a 
-solid  product  with  alkaline  reaction,  and  probably  possessing 
the  composition  of  hexamethylenetetramine,  being  formed. 

Dimethylamine  absorbs  nitrogen,  splitting  off  water  in  ratios 
that  likewise  indicate  the  formation  of  hexamethylenetetramine. 

Trimethylamine. — This  substance,  by  absorbing  a  corre- 
spondingly greater  quantity  of  nitrogen,  also  seems  to  lead 
to  the  same  compound. 

Ethylamine  does  not  react  with  nitrogen,  but  it  gives  off 
a  quantity  of  hydrogen  which  indicates  the  formation  of  a 
body  homologous  to  hexamethylenetetramine. 

Normal  Propylamine  absorbs  nitrogen  and  gives  off  hydro- 
gen. The  course  of  the  reaction  indicates  the  formation  of 
tetr amines,  which  are  derived  from  methyl-  and  ethylamine. 

Iso-Propylamine  shows  the  same  behavior  as  the  normal 
compound. 

Allylamine  develops  hydrogen,  but  neither  absorbs  nor  splits 
off  nitrogen.  The  reaction  product  has  a  strong  odor  of  piperi- 
dine  and  perhaps  the  composition  C9Hi5N3  or  Ci2H2oN4. 

1  Compt.  rend.  126,  775  (1898). 


THE  SILENT  ELECTRIC  DISCHARGE.  285 

Aniline,  Methylaniline,  Benzylamine,  the  Toluidines,  Pyridine, 
and  Piperidine  take  up  nitrogen.  Experimental,  essential  facts 
for  determining  the  nature  of  the  resulting  products  are 
lacking. 

Ethylenediamine. — The  volume  of  this  compound  is  rapidly 
increased  by  the  action  of  the  silent  electric  discharge.  Hydro- 
gen is  primarily  developed,  with  some  ammonia,  nitrogen,  and 
methane  or  ethane.  Absorption  of  nitrogen  and  ammonia  soon 
occurs,  and  hydrogen  is  split  off.  In  the  second  stage  the 
formation  of  condensation  products  (polyamines)  presumably 
predominates,  while  in  the  first  period  the  decomposition  of 
the  material  started  with  prevails. 

Propylenediamine  behaves  precisely  like  ethylenediamine. 

Phenylenediamine  (m-  and  p-),  Benzidine  and  Nicotine  absorb 
very  little  nitrogen. 

Acetamide  and  Glycocoll  absorb  little  nitrogen,  and  the 
quantity  of  the  latter  seems  to  depend  upon  the  nitrogen  ab- 
sorption capacity  of  the  respective  acids. 

Sulphocarbamide  remains  unchanged. 

Nitriles  (acetonitrile,  benzonitrile,  tolunitrile,  benzyl  cya- 
nide) absorb  nitrogen,  the  last  three  by  direct  addition  without 
giving  off  another  element,  while  acetonitrile  gives  hydrogen 
and  some  methane. 

Aldoxime  (CH3  •  CH :  N  •  OH)  combines  with  nitrogen  and 
splits  off  water. 

Phenylhydrazine  is  slightly  decomposed,  splitting  off  hydro- 
gen and  nitrogen. 

Nitromethane  is  fundamentally  broken  up,  presumably  by 
internal  oxidation,  and  with  formation  of  condensed  products; 
hydrogen,  oxygen,  carbonic  acid,  and  nitrogen  are  developed. 

Nitroethane,  unlike  the  last-mentioned  compound,  absorbs 
nitrogen.  The  behavior  of  nitromethane  corresponds  to  that 
of  formic  acid,  and  that  of  nitroethane  to  that  of  acetic  acid. 

Nitrobenzene  takes  up  little  nitrogen. 

The  following  substances  were  also  investigated:  • 

Pyrrol,  Indol,  Indigotin,  Azobenzene,  and  Albumens,  all  ab- 
sorbing nitrogen. 


286         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

Thiophene. — This  compound  under  the  influence  of  the 
electric  discharge  absorbs  as  much  as  8.6  per  cent  of  its  own 
weight  of  nitrogen,  (C4H4S)2N  being  formed  (Berthelot).1 

The  following  conclusions  can  be  drawn  from  Berthelot 's 
observations: 

1.  All  the  investigated  alcohols  fix  nitrogen,  forming  amido- 
like  substances. 

2.  The  aliphatic  alcohols  thereby  lose  hydrogen  (excepting 
allyl  alcohol),  an  atom  of   nitrogen  replacing  a  molecule   of 
hydrogen. 

3.  The  loss  of  hydrogen  is  related  to  the  behavior  of  the 
hydrocarbons,  which  form  the  basis  of  the  alcohols,  when  the 
former  are  subjected  to  the  same  conditions. 

4.  Phenols  bind  nitrogen  in  varying  proportions,  but  without 
giving  off  hydrogen. 

5.  The    isomeric    aliphatic    alcohols    behave    alike.    They 
thus  differ  from  the  three  dihydroxybenzenes. 

6.  All  aldehydes  bind  nitrogen  by  forming  condensation 
products.    Amines  or  amides  are  produced.    These  are  closely 
related  to  the  ammonia  derivatives  of  the  aldehydes,  particularly 
the   glycosins,   glyoxalines,   and,  polyamines  containing   little 
hydrogen. 

7.  Organic   acids,   just   like   the   alcohols,   aldehydes,   and 
hydrocarbons,  generally  combine  with  nitrogen,  but  no  hydro- 
gen, or  but  very  little,  is  split  off.     Only  phthalic  acid  and 
fumaric  (contrary  to  maleic)  acid  do  not  absorb  nitrogen. 

8.  Most  of  the  investigated  nitrogenous  compounds  absorb 
an  additional  quantity  of  nitrogen,  and  polyamines,  polyamides, 
and  condensation  products  seem  to  be  produced.     Exceptions, 
which  do  not  show  this  behavior  of  absorbing  nitrogen,  are: 
ethylamine,     allylamine,     phenylhydrazine,     sulphocarbamide, 
ethylenediamine,    and    propylenediamine.     Methylamine    and 
nitromethane  even  give  off  nitrogen;   this  is  probably  due  to 
the  low  percentage  of  carbon. 

9.  Aliphatic  nitrogen-containing  compounds  in  taking  up 

1  Ann,  chim.  phys.  11,  35  (1897). 


THE  SILENT  ELECTRIC  DISCHARGE. 


287 


nitrogen  lose  about  as  much  hydrogen  as  their  corresponding 
hydrocarbons  and  alcohols.  Compounds  are  produced  whose 
cyclic  character  becomes  more  pronounced  with  an  increasing 
number  of  carbon  atoms  in  the  original  molecules.  Exceptions 
to  this  rule  are  compounds  rich  in  oxygen,  like  nitroethane  and 
glycocoll.  • 

10.  Cyclical  compounds  in  absorbing  nitrogen  do  not  give 
off    hydrogen    any    more    than    cyclical    hydrocarbons    and 
phenols.     Piperidine,  on  the  contrary,  being  a  hydrated  com- 
pound, loses  hydrogen  in  absorbing  nitrogen,  just  like  aliphatic 
substances. 

11.  All  compounds  taking  up  nitrogen  by  simple  addition — 
without  giving  off  hydrogen — i.e.,  hydrocarbons,  alcohols,  alde- 
hydes, acids,  and  bases,  when  subjected  to  the  influence  of  the 
silent  discharge,  yield  substances  which  behave  like  amides  or 
amines.     Since  the  formation  of  these  substances  cannot,  of 
course,  be  based  upon  a  substitution  of  NH2,  NH,  or  N  in  place  of 
hydrogen,  we  must  ascribe  cyclic  constitutions  to  the  products 
obtained. 

12.  The  following  table  shows  a  comparison  of  polyamines 
formed   from  hydrocarbons,  alcohols,  and  bases  by  reaction 
with  nitrogen  through  the  influence  of  the  discharge.     The 
formulae  of  the  reaction  products  are  not  rational  ones,  but 
merely  arranged  in  such  a  way  that  the  quantities  of  the  separate 
elements  in  the  molecule  always  refer  to  four  nitrogen  atoms. 
This  is  done  to  express,  in  a  comparable  manner,  the  atomic 
relations  between  the  elements  in  the  polyamines. 


Composition  of  Polyamines  formed  from 

Hydro- 
carbons. 

Alcohols. 

Bases. 

Primary. 

Secondary. 

Tertiary. 

Methane  Series 
Ethane  Series 
Propane  Series 
Allyl  Series 

C8H12N4 

C16H32N4 
C15H,8N4 
CaoH^N, 

C8H.6N4,4H2O 
C8H8N4,4H2O 
C12H16N4,4H20 
C18H20N4,6H20 

C6H12H4 
C4H16N4 
C9H]8N4 
C12l£N4 

C6H12H4 
C4H12N4 
C6HI6N4 

C.HnN4 

:288         ELECTROCHEMISTRY   OF  ORGANIC  COMPOUNDS. 

The  following  relations  result  from  the  tables: 
For  an  equal  weight  of  nitrogen  the  condensation  of  the 
hydrocarbon  residue  combined  with  the  nitrogen  increases  in 
the  transition  from  derivatives  of  hydrocarbons  to  those  of  the 
alcohols,  excepting  the  polyamines  resulting  from  the  methane 
series.  This  is  very  evident  if  the  composition  of  the  men- 
tioned hydrocarbon  residues  is  referred  to  an  equal  number  of 
carbon  atoms.  The  same  increase  is  found  if  we  pass  from 
the  derivatives  of  the  alcohols  to  those  of  the  primary  bases; 
excepting  the  compounds  of  the  ethane  series.  This  condensa- 
tion is  twice  as  large  with  the  products  from  diamines  as  with 
those  from  monamines. 

2.  BEHAVIOR  OF  VAPORS  TOWARDS  TESLA  CURRENTS. 

A  few  remarks  may  be  made  here  concerning  observations 
in  a  realm  which  promises  to  become  especially  important  for 
theoretical  organic  chemistry.  It  has  been  known  for  some 
time  that  highly  rarefied  gases  or  vapors,  when  subjected  to 
the  action  of  highly  tensioned  electric  vibrations,  become 
luminous.  Hemptinne,1  by  using  Tesla  currents  and  organic 
substances,  has  recently  taken  up  the  subject  of  the  relation 
between  luminosity  and  chemical  action  and  the  dependence 
of  the  phenomena  upon  the  pressure.  He  found  that  the 
luminosity  of  the  various  substances  in  the  arrangement  of  Tesla 
is  dependent  upon  the  pressure.  A  perceptible  decomposition 
occurs  from  the  beginning  of  the  luminosity. 

A  connection  exists  between  the  pressure  at  which  the 
light  effects  of  organic  substances  begin  and  their  molecular 
weights;  but  these  relations  have  not  yet  been  sufficiently 
explained. 

H.  Kaufmann  2  has  made  extensive  investigations  concern- 

1  Ztschr.  f.  phys.  Chemie  22,  358;  23,  483  (1897);  Bull,  de  1'Acad.  roy.  de 
Belg.  11,  775  (1902). 

2  Ztschr.  f.  physik.  Chem.  26,  719  (1898);  27,  519  (1898);  28,  673  (1899); 
Ber.  d.  deutsch.  chem.  Gesellsch.  33,  1725  (1900);    34,  682  (1901);  35,  473, 
5668  (1902);  36,  561  (1903). 


THE  SILENT  ELECTRIC  DISCHARGE.  289 

Ing  the  luminosity  of  organic  vapors  under  the  influence  of  Tesla 
currents  at  atmospheric  pressure.  He  was  thus  enabled  to  for- 
mulate a  series  of  remarkable  laws. 

His  experiments  were  arranged  in  the  following  manner : 

The  electric  field  in  which  the  vapors  are  excited  to  lumi- 
nosity is  produced  by  a  Tesla  transformer,  on  the  inside  of  a  some- 
what wide  test-tube  which  has  been  converted  into  an  ozonizer. 
The  outer  layer,  5  cm.  high  and  consisting  of  thin  sheet  copper, 
is  wrapped  half  way  up  around  the  test-tube;  the  outer  layer 
has  a  narrow  vertical  slit  for  conveniently  observing  the  inside 
of  the  tube.  The  inner  coat,  of  mercury  or  tin,  is  placed  in  a 
small,  narrow  glass  tube,  which  is  kept  rigid  and  exactly  in  the 
axis  of  the  test-tube  by  a  stopper  closing  the  latter.  The 
stopper  also  supports  a  return-condenser  arrangement,  usually 
a  rising  tube.  The  substances  to  be  investigated  are  placed 
in  a  solid  or  liquid  state  in  the  test-tube,  and  the  whole  tube 
is  then  filled  with  vapor  by  vigorous  boiling. 

Some  unimportant  changes  in  the  arrangement,  such  as 
lowering  the  layers,  etc.,  are  made  with  very  difficultly  volatile 
substances  and  such  that  readily  char. 

The  luminous  phenomena  in  these  ozonizers  occur  in  the 
shape  of  more  or  less  wide,  colored  bands  of  light,  mostly  in  a 
horizontal  and  radial  direction.  Non-luminous  vapors  either 
remain  wholly  dark  or  become, — this  is  oftener  the  case, — 
interspersed  with  green-colored  "  sparks.  The  sparks  very 
rapidly  decompose  the  vapors,  precipitating  carbonaceous 
substances;  the  luminosity  itself,  on  the  contrary,  produces 
only  extremely  trifling  changes  in  the  substances. 

The  color  of  the  luminous  effects,  in  the  majority  of  cases, 
is  violet,  with  numerous  gradations  between  blue  and  red, 
rarely  yellow  and  green. 

The  hitherto  observed  regularities  refer  to  the  vapors 
emitting  the  first-mentioned  colors.  We  shall  emphasize  only 
a  few  points  among  the  great  number  of  observations: 

1.  Aromatic  substances  usually  possess  'an  extraordinarily 
higher  luminosity  than  aliphatic  compounds.  However,  simple 
aromatic  hydrocarbons  like  benzene,  its  homologues  and  benzene 


290         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

derivatives,  possessing  two  or  more  nuclei  linked  by  aliphatic 
residues,  are  either  non-luminous  or  only  slightly  so.  But 
hydrocarbons  containing  two  or  more  directly  linked  benzene 
nuclei  like  diphenyl,  carbazol,  and  condensed  nuclei  like  naph- 
thalene, anthracene,  and  phenanthrene  show  a  brilliant  violet 
luminosity. 

2.  Substituents  exert  a  powerful  influence  upon  the  light 
effects.     The    introduction    of    several   hydroxyl   groups    into 
aromatic    hydrocarbons    of    one    nucleus    produces    luminous 
effects  which  do  not  occur  with  only  one  hydroxyl  group  in  the 
molecule.     The  amino-group  always  excites  luminosity  even 
in  mono-nuclear  hydrocarbons.     The  effect  of  the  amino-group 
often  enforces  that  of  the  hydroxyl  group,  thus  aminophenols 
produce  luminous  effects  which  are  often  very  intense. 

3.  Acetyl,  benzylidene,  nitro-groups,  the  halogens,  chlorine, 
and  bromine,  and  the  carboxyl  group,  on  the  contrary,  con- 
siderably decrease  the  luminosity,  sometimes  completely. 

Kaufmann  seeks  to  employ  these  facts  for  obtaining  an 
insight  into  the  ring  system  of  benzene.  Instead  of  using  the 
term  "  constitution,"  he  uses  that  of  "condition,"  and  shows 
that  in  the  luminous  compounds  the  benzene  nucleus  is  in  an 
unstable  condition,  one  in  which  it  is  disposed  to  change  into 
a  quinone-like  structure.  The  condition  of  the  benzene  nucleus, 
determined  by  the  chemical  behavior  of  the  ring,  changes  from 
substance  to  substance  in -the  greatest  variety.  These  condi- 
tions have  possibilities  which  are  represented  by  the  Kekule, 
the  diagonal  (Glaus  and  Korner),  and  the  Dewar  formula  with 
only  one  para-bond.  The  condition  characterized  in  the  first 
formula,  according  to  Baeyer's  investigations,  is  found  in 
phloroglucin;  the  diagonal  formula  agrees  excellently  for  phthalic 
acid;  and  the  Dewar  formula,  for  instance,  for  dime  thy  1-p- 
phenylenediamine . 

The  conditions  for  most  of  the  benzene  derivatives  differ 
from  these  three  limiting  conditions  and  assume  mostly  an 
intermediate  position  which  approximates  more  or  less  that  of 
the  one  or  other  limiting  condition. 


THE  SILENT  ELECTRIC  DISCHARGE.  291 

The  luminosity  caused  by  the  action  of  Tesla  currents  indi- 
cates that  the  ring  of  the  respective  substance  exists  in  Dewar's 
condition ;  the  stronger  the  luminosity  the  more  pronounced  the 
latter  must  be. 

The  one  para-bond  in  Dewar's  ring  is  unstable,  and  is  char- 
acterized by  the  fact  that  it  can  easily  be  broken  down  by 
oxidizers;  it  thus  differs  from  the  three  para-bonds  of  the  two 
other  formulae. 

4.  In  the  aliphatic  series  Tesla  currents  are  absorbed  and 
converted  into  light  by  the  vapors  of  aldehydes  and  ketones; 
the  carbonyl  group  is  the  sole  carrier  of  the  luminosity.  The 
latter  disappears  with  derivatives  of  aldehydes  and  ketones 
which  do  not  have  the  carbonyl  group.  The  luminosity  de- 
creases: Firstly,  with  increasing  number  of  carbon  atoms  (intro- 
duction of  methyl  groups);  secondly,  with  the  entrance  of  a 
carboxethyl  group;  and  thirdly,  especially  in  the  presence  of 
a  phenyl  residue  (benzaldelryde,  acetophenone,  etc.,  show  no 
luminous  effects).  Ring  ketones  without  a  double  bond  be- 
tween carbon  atoms  can  be  luminous;  such  with  double  bonds 
cannot. 

Kaufmann  explains  the  luminosity  of  aldehydes  and  ketones 
by  the  supposition  that  the  carbonyl  group,  the  carrier  of  the 
luminous  effects  in  those  substances,  can  occur  in  various  states 
or  conditions,  like  the  benzene  nucleus.  Only  such  bodies 
which  have  the  atoms  of  the  carbonyl  group  loosely  bound 
-and  in  a  reactive  state  can  show  luminosity.  Reactability 
and  luminosity  run  parallel.  The  latter  is,  hence,  present  in 
aldehydes  and  ketones,  but  not  in  acids,  acid  anhydrides,  esters, 
and  amides,  all  of  which  contain  the  same  group  but  in  a  con- 
dition of  extremely  trifling  readability;  or,  we  can  say,  the 
atoms  of  this  group  are  firmly  bound. 

The  luminosity  of  vapors  under  the  influence  of  Tesla  oscilla- 
tions is  undoubtedly  closely  related  to  the  constitution  of  the 
substances.  It  also  seems  true  that  a  continuous  transition 
from  the  non-luminous  to  the  luminous  vapors  takes  place,  so  that 
only  quantitative,  but  no  substantial,  differences  exist  between 


292         ELECTROCHEMISTRY  OF  ORGANIC  COMPOUNDS. 

the  conditions  characterized  by  the  luminosity.  In  order  tc 
obtain  a  better  understanding  of  the  relations,  it  is  necessan; 
to  measure  these  phenomena  and,  on  the  basis  of  quantitative 
determinations,  to  seek  determinative  connections,  just  as, 
for  instance,  has  been  done  in  the  case  of  the  conductivity  of 
electrolytes. 


LIST  OF  AUTHORS. 


Aarland,  115,  116 

Abresch,  168,  173,  178 

Ach,  129,  130 

Ahrens,  74,  121,  192,  193,  216,  218, 

219 

Akerberg,  33,  38,  106 
Alefeld,  202 
Alessi,  104,  105 
Almeida,  57,  59 
Always,  182 
Andrews,  247 

Bach,  76 

Baillie,  119,  129,  215,  218 

Balbiano,  104,  105 

Bamberger,  146,  158 

Bartoli,  55,  59,  64,  77,  119,  199 

Becquerel,  59,  229 

Berl,  82 

Berthclot,    118,    244,   245,   246,247, 

250,  266-279 
Bichat,  263 
Billitzer,  56 
Biltz,  204 
Binz,  A.,  216 
Bizzarini,  65 
le  Blanc,  46 
Bolton,  250 

Bourgoin,  77,  79,  81,  104,  106,  109- 
'  112,  113-116,  117,  211,  212,  219- 

221 

Bouveault,  111 

Bottens,  Pauchand  de,  49,  134,  152 
Brand,  70,  74,  141,  204,  205,  207-  208 
Brandon,  220 
Brazier,  92,  93 
Bredig,  233,  238,  250 
Bredt   225 

Brester,  68,  77,  90,  116,  211,  213 
Brislee,  33 

Brodie,  245,  266,  267 
Brown,  76,  102,  103,  105,  107,  110, 

113,  114,  212,  213,  225 
Brunner,  30,  33,  58,  60,  63 


Buff,  238,  244,  245,  247,  248,  251 
Bunge,  65,  85,  87,  104,  199,  201, 

Campani,  65 
Caspari,  21 
le  Chatelier,  239 
Chilesetti,  143,  144 
Clark,  110 
Classen,  104,  201 
Clement,  137,  156,  184 
Coehn,  22,  23,  55,  56,  76 
Collie,  266 
Connel,  57,  59 
Constan,  76 
Coppadoro,  112 
Cormack,  227 
Coughlin,  61,  71 

Dalton,  244,  245 
Davy,  247,  252 
Dehe>an,  57,  59 
Despretz,  81 
Destrem,  248 
Dieterle,  173 
Dorrance,  178 
Drechsel,  230,  231 
Dumas,  229 
Dupre",  81 


Ehrenfeld,  75 

Eckstein,  227 

Elbs,  4,  58,  60,  63,  70,  74,  81,  85r 
136,  138-142,  150,  154,  158-175- 
179,  183,  186-189,  204  205,  207,. 
208 

Escherich,  208 

Etard,  200 

Ewers,  85,  87,  90 

Faraday,  30,  234 
Fichte,  173 
Folsing,  196 
Forster,  61,  83 
Friedel,  69,  226 

293 


294 


LIST  OF  AUTHORS. 


Friedrichs,  78, 101, 105,.133,  211,  213 

Gans,  229 

Gasparini,  109 

Gattermann,  10,  133,  136,  137,  138, 

156,  157,  164,  168-175,  177,  183, 

184,  186,  187,  191 
Gay-Lussac,  119,  246 
Gerdes,  230,  231 
Gilmour,  251 
Glaser,  47 
Goecke,  118,  170 
Goldschmidt,  H.,  32,  35 
Goppelsroder,  194,  195,  209,  216 
Gossleth,  92,  93 
Gruszkiewicz,  246 
Gunn,  O'Brien,  68 
Guntz,  263 
Guthrie,  65,  103 

Haber,  10,  34,  37,  48,  51,  143,  146, 

147,  151,  154,  155,  158,  163,  238, 

252 

Habermann  57,  58,  59 
Hagenbach,  216 
Hamonet,  87,  89,  96,  98,  99 
Hansen,  76 
Hauser,  214 
Haussermann,  136, 142, 154, 158, 161, 

168,  169,  176,  177,  187 
Heider,  168,  172,  175' 
Heilpern,  133 

Hemptinne,  264,  267,  270-279 
Renault,  O.  Dony-,  28,  47,  58,  60,  62 
Henderson,  226 
Herz,  60 
Hittorf,  65 
Hof,  181,  188 
Hofer,  69,  78,  82,  84,  86,  89,  96,  97, 

100,  101,  103,  111,  116,  215,  249 
Hofmann,  238,  244,  245,  247,  248, "251 
Hostmann,  183,  203 
Huntington,  246 

Jahn,  58,  76,  77,  79,  86 

Jaillard,  57,  59 

James,  209 

Joist,  256 

Jovitschitsch,  264,  266,  269,  270 

Jurgensen,  234 

Kampf,  81 

Kaufmann,  181,  203,  204,  207,  209, 

28S 

Keiper,  189 

Ke'kule",  76,  80,  109,  115,  116 
Kempf,  133,  173 
Kendall,  154 
Klappert,  176 
Klein,  184 


Klobukow,  76,  248 

Knudson,  67 

Kolbe,  65,  76,  79,  81,  85,  88,  90,  97 

Komppa,  114 

Kopp,  159,  160,  168,  171,  172,  177 

Koppert,  137,  156,  169 

Kraszler,  131 

Kratz,  85 

Kremann,  173,  187 

Lebhardt,  172,  213 

Langley,  239 

Lapschin,  78 

Lassaigne,  220,  229 

Lassar-Coehn,  81 

Law,  134 

Lecher,  273 

Lees,  223 

Legler,  238,  253 

Lepsius,  238 

Lieben,  76 

Liebermann,  133 

Liebmann,  202 

Lob,  10-20-22,  23,  43,  49,  52,  80,  95, 
138,  139,  143,  146,  151,  154,  156, 
157,  158,  160,  161,  162,  163,  164- 
173,  175,  177,  181,  183,  188,  196, 
197,  199,  201,  211,  213,  241,  250, 
253,  254,  257,  258,  259,  266,  267 

Lobe,  72 

Lommel,  247 

Losanitsch,  264,  266,  269,  270 

Liidersdorf,  59 

Lumsden,  114 

Luther,  33 

Maquenne,  270,  273,  274,  277 

Marie,  118,  213 

Matteuci,  211 

McCoy,  64 

Meissner,  74 

Melly,  247 

Merzbacher,  134  ' 

Messinger,  201 

Mettler,  212 

Mewes,  61 

Meyer,  E.  v.,  245 

v.  Miller,  68,  86,  95,  96,  97,  101,  103, 

106,  108,  111,  116,  117,  213,  215 
Mixter,  245 

Moest,  78,  82,  84,  86,  89,  111,  208 
Moissan,  237,  250 
Moller,  191,  192 

Moore,  15,  20,  49,  53,  85,  143,  151 
Monfang,  222 
Miiller,  22,  23,  72,  163 
Mulder,  69 
Miillerus,  216 

Mulliken,  74,  76,  103,  108,  117 
Murray,  82 


LIST  OF  AUTHORS. 


295 


Muthmann,  249 

Naumann,  24,  25,  221,  222 
Nernst,  17,  21,  30,  33,  35,  37,  45 
Noyes,  30,  137,  156,  178,  184 

Oettel,  4,  106 
Oswald,  45 

Palmaer,  118 

Papasogli,  55,  59,  64,  77,  119,  199 

Paschen,  239 

Perkin,  134,  202,  246 

Perlin,  210 

Petersen,  78,  82,  89,  90,  93,  106,  110, 

113,  114 

Perrot,  119,  247,  248 
Pfeffermann,  67,  73,  203-205 
Phipson,  267 
Pierron,  169 
Piguet,  83 
Pinnow,  179 
Pissarshewski,  99 
Pommerehne,  220,  221 
Prevost,  229 
Puls,  134 

Quet,  M.,  247 
Quincke,  234 

Readmann,  251 

Reboul,  112,  113 

Reindl,  122,  123 

Renard,  57,  58,  63,  64,  65,  66,68, 

77,  104,  133,  134 
Richard,  70 
Riche,  59,  60 
Rockwell,  100 

Rohde,  169,  176,  177,  178,  180,  191 
Rohland,  93,  94 
Romppa,  225 
Russ,  34,  37,  53,  151 
Rotundi,  193 
Royer,  50,  76,  105 

Sachs,  173 

Salzer,  77,  106 

Sand,  62 

Schall,  6,  80,  130,  131,  184,  211 

Schlagdenhauffen,  119 

Schmidt,  72,  177,  192,  207 

Schmitt,  135,  169,  171 

Schmitz,  27,  225 

Schonbein,  59,  119 

Schwerin,  234 

Sebor,  196,  213 

Shedden,  223 

Shields,  115 

Silbermann,  140,  162,  163 


Singer,  62 

Slawik,  213 

Slosse,  268,  270 

Smith,  E.  F.,  4,  81,  110,  134 

Sollmann,  193 

Sonneborn,  178 

Stern,  119,  120 

Stone,  64 

Straub,  158,  160 

Strobel,  192 

Sulzberger,  173 

Szarvasy,  196 

Tafel,  14,  22,  23,  27,  43,  52,  67,  70, 
73,  78,  101,  105,  119,  122,  123, 
125,  126,  128,  129,  143,  144,  145, 
191,  192,  203-205,  212,  213,  215, 
218,  221,  222,  225,  227 

Tait,  247 

Teeple,  71,  72 

Thenard,  245,  270 

Thomas,  119    ' 

Tichanowitsch,  78,  203 

Tommasi,  68 

Troeger,  85,  87,  90 

Truchot,  248 

Ullmann,  173 
Ulpiani,  109 
Ulsch,  69 

Vanzetti,  112 

Vaubel,  202 

Violle,  239 

Voigt,  64,  177,  190,  191,  195 

Vortmann,  201 

Votocek,  196 

Walker,  76,  97,  102,  103,  105,  107, 
108,  110,  113,  114,  212,  213,  225- 
227 

v.  Wartha,  216 

Weems,  76,  100,  101,  103,  108,  118 

Weinschenk,  122,  128 

Weith,  119 

Weizmann,  191,  210 

Werther,  64 

Whitney,  30 

Widera,  193 

Wiedemann,  81 

Wilde,  245,  247,  249 

Wogrinz,  183 

Wohlfahrt,  173,  186 

Wolff enstein,  220 

Wiirtz,  92,  94,  95,  103 

Zehrlant,  200 
Zenisek,  196 
Zschocke,  172,  213 


INDEX. 


Acetaldeyhde,  56,  59,  60,  07,  87,  97, 
98,  99,  100,  111,  116,  253,  270,  270 

Acetaldehyde  and  nitrogen,  282 

Acetamide  and  nitrogen,  285 

Acetanilide,  196,  215 

Acetates,  79,  81,  82 

Acetic  acid,  57,  60,  63,  64,  69,  78,  99, 
100,  111,  245.  248,  251,  253,  278 

Acetic  acid  and  nitrogen,  283 

Acetic  aldehyde,  see  Acetaldehyde 

Acetic  anhydride,  80 

Acetic  esters,  59,  78,  84,  101,  278,  283 

Acetoacetic  acid,  100 

Acetoacetic  acid  and  nitrogen,  284 

Acetoacetic  ester,  100 

Acetone,  63,  69,  98,  248,  277 

Acetonedicarboxylic  acid,  101 

Acetonephenylhydrazone,  73 

Acetonitrile,  121 

Acetonitrile  and  nitrogen,  285 

Acetonylacetone,  102 

Acetophenone,  204 

Acetophenone-oxime,  204 

Acetophenonepinacone,  204 

Acetoxime,  72 

Acetylacetone,  74 

Acetylacetonedioxime,  74 

Acetylaminophenol,  223 

Acetyl  chloride,  256 

Acetyl  disulphide,  85 

Acetylene,  56,  110, 115,  118,  211,  244, 
245-250-271,  278 

Acetylene  and  nitrogen,  271 

Acetylmalonic  acid,  101 

Acetylmethylaminophenol,  224 

Acetyl  pyrrolidone,  121 

Acetyltetrahydroquinoline,  218 

Acetyltoluidine,  215 

Acid  amides,  118,  215 

Acidnitroamides,  166 

Acids,  75,  277 

Acids  and  nitrogen,  283 

Acid  superoxides,  80 

Acid  supersulphides,  80 


Aconitic  acid,  118 

Acridine,  259 

Acrolem,  64,  245 

Acrylic  acid,  64,  116 

Acrylic  ester,  110 

Adenine,  127 

Adipic  acid,  111,  114,  232 

Adipic  diethyl  ester,  112 

Adipic  ethyl  ester,  110 

Albumen,  229,  233 

Albumen  and  nitrogen,  285 

Alcohols,  62,  202,  211,  273 

Alcohols  and  nitrogen,  279 

Aldehydecopellidinehydrazine,  1 93 

Aldehydephenylhydroxylamine,  182 

Aldehyde  resin,  59 

Aldehydes,  66,  157,  202,  276 

Aldol,  98 

Aldol  and  nitrogen,  283 

Aldoxime  and  nitrogen,  285 

Aliphatic  compounds,  54 

Alizarin,  133,  195,  210 

Alizarinamide,  191 

Alizarin-bordeaux,  133 

Alizarin-cyanine,  133 

Alkaloids,  21 7 

Alkyl-disulphides,  65 

Alkyl-hydroxylamines,  56 

Allocampholytic  acid,  226 

Allocamphoric  acid,  226 

Allocamphoric  ester,  227 

Alloxan,  124 

Alloxantin,  124 

Allyl  alcohol,  276 

Allyl  alcohol  and  nitrogen,  281,  282 

Allylamine  and  nitrogen,  284 

Allylene,  271 

Allylene  and  nitrogen,  271 

Alternating  currents,  230 

Amifloacetone,  74 

Amidoacetophenone,  183 

Amidoalizarin,  210 

Amidoanthraquinone,  191 

Amidoazobenzene,  178 

297 


298 


INDEX. 


Amidoazo-compounds,  194 

Amidobenzophenone,  183 

Amidobenzyl  alcohol,  170 

Amidocaproic  acid,  193 

Amidocoumarin,  185 

Amidocresol,  168,  175 

Amidocresolsul  phonic  acid,  187 

Amidocresotinic  acid,  185 

Amidodihydropurin,  130 

Amidodimethylaniline,  178 

Amidodiphenyl,  173 

Amidodiphenylamine,  180 

Amidohydroquinone,  196 

Amidonaphtholsul phonic  acids,  191 

Amidonaphthyl  etnyl  ether,  191 

Amidonitrophenol,  176 

Amidooxyacetophenone,  183 

Amidooxycinnamic  acids,  185 

Amidooxydiethylaniline,  179 

Amidooxypurin,  130 

Amidooxyquinoline,  193 

Amidooxyterephthalic  acid,  186 

Amidooxytoluquinoline,  193 

Amidophenanthrenequinone,  1 92 

Amidophenols,  136,  137,  138,  149, 
154,  150-176 

Arnidophenol  sulphate,  137 

Amidophenolsulpnonic  acids,  137, 
156,  176,  184,  187 

Amidophenylhydroxylamine,  164 

Amidophenyltolyl  ether,  177 

Amidophthalic  acid,  186 

Amidopurin,  130 

Amidosalicylic  acid,  184 

Amidosulpnonic  acids,  187 

Amido valeric  acids,  192 

Amidoxylenol,  172 

Amines,  57,  67,  73,  118,  121,  203, 
215,  216,  etc. 

Amino,  see  Amido 

Ammonia,  246 

Ammonium  carbamate,  230 

Ammonium  dithiocarbamate,  131 

Amyl  alcohols,  63,  93 

Amyl  caproate,  92,  93 

Amylenes,  93 

Amylhydrocinnamic  ester,  214 

Amyloxypropionic  acid,  98 

Anhydroamidobenzyl  alcohol,  158 

Anhydrohydroxylaminebenzyl  alco- 
hol, 158 

Anilidoinduline,  196 

Aniline,  136-162-163,  176,  193-198, 
203-246,  249,  254,  258 

Aniline  and  nitrogen,  285 

Aniline  black,  195 

Anisidine,  176 

Anodic  depolarizers,  8 

Anodic  processes,  27 

Anthranil,  258 


Anthranilic  acid,  184,  258 
Anthranols,  210 
Anthraquinone,  133,  195,  209 
Anthrones,  210 
Argon,  272 
Anstol,  201 

Aromatic  compounds,  132 
Atropine,  219 
Attackable  electrodes,  18 
Azoacetophenone,  183 
Azoanisol,  176 
Azobenzamide,  186 
Azobenzene,  133,  136-159-163 
Azobenzene  and  nitrogen,  285 
Azobenzoic  acid,  181,  183,  188 
Azobenzoic-acid-benzyl  alcohol,  188 
Azobenzonitrile,  186 
Azobenzophenone,  183 
Azobenzyl  alcohol,  181,  188 
Azo-compounds,  194 
Azo-dyes,  197 
Azophenine,  196 
Azophenol,  176 
Azophthalic  acid,  186 
Azostiltx^nedisulphonic  acid,  187,  18* 
Azotoluene,  136,  168,  171 
Azotoluenebenzoic  acid,  189 
Azoxyacetophenone,  183 
Azoxyanisol,  176 
Azoxybenzaldpxime,  182 
Azoxybenzamide,  186 
Azoxybenzene,  136-1 43-147-168-1 6c 
Azoxybenzoic  acid,  181,  183,  184 
Azoxybenzonitrile,  186 
Azoxybenzophenone,  183 
Azoxybenzyl  alcohol,  181 
Azoxydiphenyl  ether,  177 
Azoxylene,  172 
Azoxyphenanthrene,  192 
Azoxyphenyl  ethers,  177 
Azoxyphenyltolyl  ether,  177 
Azoxystilbene,  173 
Azoxystilbenedisul phonic  acid,  187 
Azoxytoluenes,  136,  168,  169,  171 
Azoxyxylenes,  172 

Barbituric  acid,  123,  124 
Benzal  chloride,  159 
Benzaldehyde,  134, 138, 157, 168, 170 

203,  212,  215,  260 
Benzaldehyde  and  nitrogen,  283 
Benzaldpxime,  203 
Benzamide,  215 
Benzene,    133,    246,    248,   251,    253. 

257 

Benzene  and  hydrogen,  272 
Benzene  and  nitrogen,  272 
Benzeneazonaphthol,  155 
Benzeneazonaphthylamine,  155 
Benzenephenylenediamine,  196 


INDEX. 


299 


Benzhydrol,  204,  205 

Benzhydrylamine,  205 

Benzidine,   136,   139,    140,   142,  160, 

161,  167 

Benzidine  and  nitrogen,  285 
Benzile,  209 
Benzilic  acid,  209 
Benzoic   acid,    134,    209,    211,    260, 

279 

Benzoic  acid  and  nitrogen,  284 
Benzoic  esters,  212 
Benzoic  ethyl  ester,  134 
Benzoin,  209,  283 
Benzoin  and  nitrogen,  283 
Benzonitrile,  121,  216 
Benzonitrile  and  nitrogen,  285 
Benzophenone,  204 
Benzophenone-oxime,  20o 
Benzophenonepinacone,  205 
Benzotrichloride,  259 
Benzoylazoxydiphenylamine,  181 
Benzoyl bisulphide,  212 
Benzoylnitrodiphenylamine,  180 


216 


Benzyl  alcohol,  134,  212,  215 
Benzylamine,  121,  203,  215,  216 
Benzylamine  and  nitrogen,  285 
Benzyl  chloride,  259 
Benzyl  cyanide,  121,  210 
Benzyl  cyanide  and  nitrogen,  285 
Benzyl  ethers,  212 
Benzylidenephenylhydrazone,  203 
Benzylidenephenylhydroxylamine, 

138,  157 
Benzylidenetolylhydroxylamine,  1 68, 

Benzylmalonic  acid,  116,  213 
Benzylpiperidine,  218 
Blood,  229 
Borneol,  225 
Bromacetone,  71 
Bromamidocresol,  175 
Bromamidophenol,  175 
Bromanilines,  156 
Brombenzene,  197 
Brombenzoic  acid,  212 
Brombenzoic  esters,  212 
Bromine,  250 
Brommaleic  acid,  115 
Bromnitrobenzene,  175 
Bromnitrotoluene,  175 
Bromoform,  60,  71,  256 
Bromstyrene,  213 
Brucidine,  223 
Brucine,  222 
Butane,  86,  87 
Butandiol  diamyl  ether,  98 
Butyl  alcohol,  74,  91 


Butyl  caproyl,  95 

Butylenes,  90,  91,  92 

Butyl  valerate,  90,  91 

Butyrates,  88,  101 

Butyric  acids,  87,  89,  231,  232,  270 

Butyric  aldehyde,  91 

Butyric  ethyl  ester,  108,  111 

Butyric  isopropyl  ester,  88 

Caffeine,  127,  129 

Camphidine,  228 

Camphidone,  228 

Campholytic  acid,  226 

Camphor,  225 

Camphor  and  nitrogen,  283 

Camphoric  acid,  225,  227 

Cumphoric-acid-imide,  227 

Camphoric  acid  and  nitrogen,  284 

Camphoric  esters,  225 

Camphothetic  acid,  226 

Cane-sugar,  68 

Caproic  acid,  92,  101,  231,  232 

Caproic  amyl  ester,  92,  93 

Caprylic  acid,  93 

Carbamic  acid,  230 

Carbamide,  230 

Carbazole,  258 

Carbides,  metal,  250 

Carbohydrates,  208 

Carbolic  acid,  see  Phenol. 

Carbon,  54,  250 

Carbon  disulphide,  245 

Carbon  disulphide  and  hydrogen,  269 

Carbon  hydroxide,  55 

Carbonic  acid,  76,  266 

Carbonic-acid  derivatives,  121 

Carbon  monosulphide,  269 

Carbon  monoxide,  267 

Carbon  monoxide  and  ammonia,  270 

Carbon  monoxide  and  dioxide,  268 

Carbon  monoxide  and  hydrochloric 
acid,  269 

Carbon  monoxide  and  hydrogen  sul- 
phide, 269 

Carbon  oxysulphide,  269 

Carbon  suboxide,  266 

Carbon  tetrachloride,  250,  255 

Carvacrol,  201 

Catalytic  influences,  24 

Cataphoresis,  233 

Cathode  material,  152,  167,  169,  171 

Cathodic  depolarizers,  7 

Cathodic  processes,  18 

Cells,  40 

Cellulose  and  nitrogen,  283 

Chloracetic  acids,  59,  85 

Chloracetone,  69,  70 

Chloral,  62 

Chloral  hydrate,  68,  255 

Chloraminophenol,  175 


300 


INDEX. 


Chloraniline,  138,  139,  140,  156,  174 

Chlorbenzene,  197 

Chlorbenzoic  esters,  21 2 

Chlor-hydrocarbons,  250 

Chlorine,  250 

Chlornaphthalene,  197 

Chlornitrobenzene,  174 

Chlornitrotoluenes,  1 75 

Chloroform,  60,  70,  253 

Chloroform  and  aniline,  254 

Chlorphenylmethylene,  259 

Chlorpropionic  acid,  87 

Chlortoluene,  197 

Chlortoluidine,  175 

Chrysamine  G,  198 

Chrysaniline,  195 

Cinchonidine,  221 

Cinchonine,  221 

Cinnamic  acid,  213 

Cinnamic  aldehyde  and  nitrogen,  283 

Cinnamic  ester,  214 

Citraconic  acid,  110 

Coca-alkaloids,  219 

Cocaine,  219 

Codeine,  220 

Collodion,  68 

Colloids,  233 

Congo,  198 

Cotarnine,  220 

Cresol,  258 

Cresotinic  acid,  201 

Crotonic  acid  and  nitrogen,  284 

Crotonic  aldehyde,  98,  116 

Cyanacetates,  85 

Cyanacetic  ester,  98 

Cyanides,  251 

Cyanogen,  121,  247,  251,  252 

Cyclohexanone,  231 

Decahexanedicarboxylic  acid,  115 
Decane,  92,  93,  95,  107 
Decanedicarboxylic  acid,  114 
Dehydracetic  acid,  284 
Depolarizers,  6,  7,  8 
Desoxy-bodies,  127,  128 
Desoxycaffeine,  129 
Desoxyguanine,  130 
Desoxyheteroxanthine,  128,  129 
Desoxytheobromine,  129 
Desoxyxanthine,  127 
Dextrine,  68 

Dextrine  and  nitrogen,  283 
Diacetyl,  100,  101 
Diacetyldiamidoazoxybenzene,  178 
Diacetylsuccinic  ester,  100 
Dial  uric  acid,  123 
Diamidoanthraquinones,  192 
Diamidoanthrarufindisulphonic  acid, 

192 
Diamidoazobenzene,  164,  177 


Diamidobenzene,  164,  178 
Diamidobenzhydrols,  208 
Diamidobutane,  123 
Diamidochrysazindisulphonic      acid 

192 

Diamidocresol,  173 
Diamidodibenzyldisulphonic  acid,  188 
Diamidodimethyloxyphenazone,  1 74. 

179 

Diamidonitrophenol,  176 
Diamidopentane,  74 
Diamidophenanthrenequmone,  192 
Diamidophenazone,  174 
Diamidophenol,  173,  176,  177 
Diamidophenyltolylmethane,  1 70 
Diamidopropane,  123 
Diamidostilbene,  173 
Diamidostilbenedisulphonic  acid,  187, 

188 

Dianilidoquinoneanil,  176 
Dianisidine-blue,  198 
Diatomic  alcohols,  63 
Diazoamido-com  pounds,  194 
Diazo-compounds,  194 
Dibasic  acids,  102 
Dibenzylacetic  acid.  214 
Di  benzyl  ketone,  208 
Dibenzylsuccinic  acid,  214 
Dibromanthraquinone,  210 
Dichloracetic  acid,  85 
Dichloracetone,  69 
Dichloraniline,  175 
Dichlormethvlene,  254 
Dichlornitrobenzene,  175 
Dichlorpropionic  acid,  87 
Dichlorpropionic   diclilorethyl   ester, 

87 

Diethylamine,  67 
Diethylammonium    diethyldithiocar- 

bamate,  131 
Diffusion  theory,  30 
Dihydroquinoline,  218 
Dihydroxylamine,  145 
Diisobutane,  90 
Diisobutyl,  91 
Diisopropyl,  89 
Dimethylamine,  284 
Dimethylaniline,  198 
Dimethylbenzaldehydes,  134 
Dimethylbenzamide,  215 
Dimethylbenzimidazole,  179 
Dimethylbenzylamine,  215 
Dimethyldiamidoazobenzene,  178 
Dimethyldiamidophenol,  178 
Dimethylethanetetracarboxylic  acid, 

108 

Dimethyloxydihydropurin,  129 
Dimethyloxypuron,  129 
Dimethyloxypurinmethylhydroxide, 

129 


INDEX. 


301 


iJimethylphenazone,  174 
Pimethylpiperylhydrazine,  193 
1  Mmethylpurons,  126 
Dimethylpyrazine,  74 
Dimethylpyrazolidine,  74 
Dimethylsuccinic  acid,  107 
Dimethyl  toluidine,  170,  171 
Dimethyltoluylenediamine,  180 
Dimethyl  uric  acids,  126 
Dimethylxanthine,  129 
Dinitroanisidine,  174 
Dinitroanthrarufindisulphonic     acid, 

192 

Dinitroanthraquinone,  192 
Dinitrobenzene,  173 
Dinitrobenzidine,  174 
Dinitrobenzoic  acid,  173 
Dinitrochrysazindisulphonic  acid,  192 
Dinitrodibenzyldisulpnonic  acid,  188 
Dinitrodiphenyl,  185 
Dinitroditolyl,  174 
Dinitroethanetetracarboxylic       acid, 

109 

Dinitronaphthalene,  191 
Dinitrophenanthrenequinone,  192 
Dinitrophenol,  176 
Dinitrostilbene,  173 
Dinitrostilbenedisulphonic  acid,  187, 

188 
Dinitrotetraethyldiamidodiphenyl, 

174 
Dinitrotetramet  hyldiamidodi  pheny  1 , 

174 

Dinitrotoluene,  173 
Dioctyl,  93 
Dioxy-acids,  96,  98 
Dioxyanthraquinone,  210 
Dioxybenzene,  232 
Dioxybenzoic  acid,  214 
Dioxybutyric  acid,  99 
Diphenol,  231 

Diphenyl,  212,  248,  249,  257 
Diphenylamine,  195,  258 
Diphenylamine  and  chloroform,  258 
Diphenylbenzene,  257 
Diphenylenediamine,  272 
Diphenylmethane,  205 
Diphenylthiocarbazide,  131 
Disulphide,  acetyl,  85 
Dithiocarbamic  acid,  131 
Dithiondisulphides,  131 
Dithymoldiiodide,  201 
Ditolylamine,  195  . 

Dodecane,  93,  95 
Dodecanedicarboxylic  acid,  115 
Dowson  gas,  246 

Electric  flame,  249 
Electrode  potential,  14 
Electrode  processes,  18 


Electrodes,  18,  51 

Electrolysis  of  mixtures,  94 

Electrolytic  processes,  10 

Electropyrogenizer,  242 

Endosmose,  electric,  233 

Eosin,  201,  202 

Ervthrite,  65 

Ethane,  59,  79, 81, 116,  271,  275,  276, 

278 

Ethane  and  carbon  monoxide,  271 
Ethane  and  nitrogen,  271 
Ethanehexacarboxylic  ester,  117 
Ethanetetracarboxylic  ester,  108 
Ether,  ethyl,  246,  247,  253 
Ethers  and  nitrogen,  281 
Ethoxybenzophenone,  206 
Ethoxybenzpinacoline,  206 
Ethyl  alcohol,  59,  97,  247,  274 
Ethyl  alcohol  and  nitrogen,  280 
Ethylamine,  57,  67,  121,  248 
Ethylamine  and  nitrogen,  284 
Ethylaminophenol,  223 
Ethylaniline,  215 
Ethylcrotonic  acid,  108 
Ethyl  cyanide,  248 
Ethyldioxysulphocarbonate,  131 
Ethylene,  81,  86,  106,  110,  116,  245, 

246,  247,  248,  252,  253,  256,  273, 

275 

Ethylene  and  nitrogen,  271,  278 
Ethylene  cyanide,  82 
Ethylenediamine  and  nitrogen,  285 
Ethylenedihydroxylamine,  73 
Ethylenelactic  acid,  98 
Ethylene  oxide  and  nitrogen,   281, 

282 

Ethyl  ether,  246,  247,  253 
Ethyl  ether  and  nitrogen,  281 
Ethyl  glycollic  ether,  97 
Ethylhydroxylamine,  57  * 
Ethylideneimine,  67 
Ethylidene  oxyethyl  ether,  59 
Ethylidene  phenylhydrazone,  67 
Ethylmalonic  acid,  108,  114 
Ethylmethylacetic  acid,  92 
Ethylphosphoric  acid,  66 
Ethyl     potassium    diethylmalonate, 

107,  108 
Ethyl  potassium  dimethylmalonate, 

107,  108 

Ethyl  potassium  ethylmalonate,  107 
Ethyl  potassium  fumarate,  115 
Ethyl  potassium  glutarate,  113 
Ethyl  potassium  maleate,  115 
Ethyl  potassium  malonate,  103,  104 
Ethyl     potassium    methylmalonate, 

107,  112 

Ethyl  potassium  oxalate,  105 
Ethyl  potassium  succinate,  112 
Ethyl  propionate,  86 


302 


INDEX 


Ethyl  pyrrolidone,  120 
Ethylsuccinic  acid,  117 
Ethyl-sulphuric  acid,  59,  60,  66 
Ethyltartaric  acid,  117 
Ethyltetrahydroquinoline,  218 
Ethyltoluidine,  215 
Ethyltrithiocarbonic  acid,  131 
Ethyl  urea,  122 
Eugenol,  202 
Excess  potential,  20,  27 
Experimental  arrangements,  44 

Flaming  discharge,  249 
Fluor-albumens,  229 
Fluorescein,  201,  202 
Formaldehyde,   57,   58,   66,   67,    76, 

96,  97,  98,  99,  117,  157,  171,  251, 

253,  267,  268,  269,  270 
Formaldehyde  and  nitrogen,  283 
Formamide,  270 
Formic  acid,  56,  63,  64,  65,  66,  68, 

69,  76,  77,  9*6,  97,  98,  99,  105-111- 

117,  231,  245,  248,  250,  253,  257, 

266,  267,  270,  277 
Formic  acid  and  nitrogen,  283 
Formic  ester,  59,  78 
Formic  ethyl  ester,  278 
Formic  methyl  ester,  278 
Formic  methyl  ester  and  nitrogen 

283 

Formyl  chloride,  256,  269 
Formylphenyl  ether,  182 
Fulminuric  acid,  109 
Fumaric  acid,  115,  284 
Furfurol  and  nitrogen,  283 

Gallaminic  acid,  214 

Gallic  acid,  202,  214 

Generator  gas,  246 

Glucose,  62,  68,  203 

Glucose  and  nitrogen,  285 

Glutaric  acid,  112,  232 

Glutaric  diethyl  ester,  112 

Glyceric  acid,  64,  98,  279 

Glyceric  aldehyde,  64,  279 

Glycerine,  64,  276 

Glycocoll  and  nitrogen,  285 

Glycol,  63,  276 

Glycollic  acid,  64,  96,  97,  105,  279 

Glycollic  aqid  and  nitrogen,  284 

Glycollic  ethyl  ether,  97 

Glyoxal  67,  73,  277 

Glyoxalic  acid,  73 

Glyoxime,  67,  73 

Glyoxylic  acid,  67,  105 

Grape-sugar,  68 

Graphitic  acid,  63,  64 

Guanine,  127,  130 

Gum  arabic,  68 


Heptane,  95 
Heptylic  acid,  93 
Heteroxanthine,  128 
Hexachlorbenzene,  250 
Hexachlorhexane,  90 
Hexamethylenetetramine,  67,  284 
Hexane,  88,  89,  101,  252 
Hexamethylethane,  92 
Hexaoxymethylene  peroxide,  253 
Hexyleneglycol,  99 
Hydantoin,  122 
Hydraciylic  acid,  99,  111 
Hydrastmine,  220 
Hydrazoanisol,  176 
Hydrazobenzene,  136-160-163 
Hydrazobenzoic  acids,  183,  184  • 
Hydrazobenzoin,  203 
Hydrazo-com  pounds,  141 
Hydrazonaphthalenesulphonic    acid, 

Hydrazophthalic  acid,  186 
Hydrazotoluene,  136,  168,  169,  171 
Hydrazoxylene,  171 
Hydroanthranols,  210 
Hydroanthraquinone,  210 
Hydrobenzom,  203 
Hydrocarbons,  54,  133,  244,  270 
Hydrocinnamic  acid,  213,  214 
Hydrocyanic  acid,  121,  245,  246,  247, 

249 

Hydrocotarnine,  220 
Hydrohydrastinine,  220 
Hydrophenoketone,  232 
Hydrophenazone,  173 
Hydroquinaldine,  219 
Hydroquinoline,  218 
Hydroquinone  133,  201,  218,  231 
Hydroquinone  and  nitrogen,  281 
Hydroquinonecarboxylic  acid,  133 
Hydroquinone  ether,  200 
Hydroquinone-p-nitrodiphenyl  ether, 

Hydrouracyl,  123,  124 
Hydroxycaffe'ine,  127 
Hydroxylamine,  57,  145 
Hydroxyl-cpmpounds,  57 
Hypoxanthine  127 
Humus  substances  and  nitrogen,  283 

Imides,  118 

Indigo  reduction,  216,  217 
Indigotin  and  nitrogen,  285 
Indol  and  nitrogen,  285 
Induline  dyes,  196 
Iodine,  250 
lodonitrobenzene,  175 
lodoform,  60,  72,  87,  119 
lodopropionic  acid,  87 
Isethiomc  acid,  66 
Isoacetyl-o-aminophenol,  223 


INDEX. 


303 


Isoamyl  alcohol,  63 
Isoamylphosphoric  acid,  66 
Isoamylsulphuric  acid,  66 
Isoamylxanthate,  131 
Isobutylacetic  ester,  112 
Isobutyl  alcohol,  91 
Isobutylcresol,  201 
Isobutylene,  92 
Isobutyl  isovalerate,  91 
Isobutylphenol,  201 
Isobutyl  valerate,  91 
Isobutyl  xanthate,  131 
Isobutyric  acid,  87,  89 
Isobutyric  aldehyde,  91 
Isobutyric  isopropyl  ester,  88 
Isoeugenol,  202 
Isohydrobenzoi'n,  203 
Isohexane,  89 
Isolauronic  acid,  227 
Isonitroacetone,  74 
Isopropyl  alcohol,  63   70,  88,  89,  276 
Isopropyl  alcohol  and  nitrogen,  280 
Isopropylamine,  73 
Isopropylamine  and  nitrogen,  284 
Isopropylpyrrplidone,  119 
Isopropylsuccinimide,  119 
Isopurons,  125,  126 
Isovaleric  acid,  63,  90 
Itaconic  acid,  115,  116 

Ketones,  66,  69,  276 
Ketones  and  nitrogen,  282 
Ketones,  aromatic,  202 
Ketonic  acids,  99 
Ketoximes,  72 

Lactic  acids,  97,  100 
Lactic  acid  and  nitrogen,  284 
Lsevulinic  acid,  100,  102 
Laevulinic  acid  and  nitrogen,  284 
Laurolene,  226 
Lead  diacetate,  81 
Lead  tetracetate,  81 
Leucaniline,  195 

Maleic  acid,  115,  284 
Maleic  acid  and  nitrogen,  284 
Malic  acid,  116 
Malic  acid  and  nitrogen,  284 
Malonic  acid,  106,  112,  231 
Malonic  ester,  117 
Malonyl  urea,  123 
Mandelic  acid,  215 
Mannite,  65,  68 
Meconic  acid,  220 
Mellogen,  64,  121 
Mellitic  acid,  120 
Mercaptans,  65 
Mercurargon  phenide,  272 


Mercuric-iodide  compounds  of  alco- 
hols, 62 

Mercury  methide,  272 

Mercury  phenide,  272 

Mesaconic  acid,  116 

Mesitylene,  134 

Mesitylenic  aldehyde,  134 

Mesityloxide,  70 

Mesoxalyl  urea,  124 

Metanilic  acid,  187 

Methane,  58,  81,  110,  244,  245,  248. 
250,  252,  253,  270,  273,  276,  277, 
278 

Methane  and  carbon  dioxide,  270 

Methane  and  carbon  monoxide,  270 

Methane  and  nitrogen,  271 

Methane  and  oxygen,  270 

Methanetricarboxylic  acid,  117 

Methodics,  40,  235 

Methoxylglycollic  acid,  97 

Methylacetate,  57,  79,  81 

Methylacrylic  acid,  108 

Methylal,  57,  97,  282 

Methyl  alcohol,  57,  83,  97,  111,  250, 
253,  268,  273 

Methyl  alcohol  and  nitrogen,  279 

Methylamine,  57,  67,  195,  248 

Methylamine  and  nitrogen,  284 

Methylaniline,  194,  285 

Methylazobenzene,  189 

Methyl  benzyl  ether,  212 

Methylcaproyl,  95 

Methylcarbonic  acid,  58 

Methyldesoxyxanthine,  128,  130 

Methyldiphenylamine,  195 

Methylene  di-p-anhydroamidobenzyl 
alcohol,  158 

Methyl  ether,  79 

Methyl  ether  and  nitrogen,  281 

Methylethyl-a-amino-/?-naphthol,  224 

Methylethylaminophenol,  224 

Methylethylketone,  74 

Methylethylketoxime,  73 

Methylethyl-/?-naphthomorpholone, 
224 

Methylethylpinacone,  74 

Methyl  formate,  57,  81 

Methylglyceric  acid,  99 

Methylglycidic  acid,  99 

Methylglyoxime,  67 

Methylhydroxylamine,  57 

Methylhydrocinnamic  acid,  212 

Methylisopurons,  126 

Methylmalonic  acid,  108 

Methylmorphine,  220 

Methylnaphthomorpholine,  224 

Methylnaphthomorpholone,  224 

Methyl  oxide,  110 

Methyloxydihydropurins,  128 

Methyloxypurin,  128 


304 


INDEX. 


Methylphenomorpholine,  224 
Methylphenomorpholone,  224 
Methylphenyl  carbinol,  204 
Methylpiperylhydrazine,  192 
Methylpropylketone,  102 
Methylpurons,  126 
Methylquinoline,  219 
Methylsuccinic  acid,  113 
Methyl-sulphuric  acid,  57,  65 
Methyltrimethylene  urea,  122 
Methyluracyl,  122 
Methyl  uric  acids,  126 
Methylxanthine,  128 
Methylxanthate,  131 
Michler's  ketone,  207 
Monobasic  acids,  77 
Monobasic  alcohol-acids,  95 
Monobasic  ketonic  acids,  95 
Monobromacetone,  09,  71 
Monochloracetic  acid,  85 
Monochloracetone,  69 
Morphine,  220 
Morpholines,  223 
Morpholones,  223 

Naphthalene,  134,  249,  251 
Naphthazarine,  191 
Naphthol,  154,  201 
Naphtholphentriazole,  190 
Naphthomorpholones,  223 
Naphthoquinone,  134 
Naphthylamine,  155,  167,  191, 195  j 
Naphthylenediamine,  191 
Nicotine,  285 

Nitranilines,  164,  166,  167,  177 
Nitriles,  118,  121,  215 
Nitriles  and  nitrogen,  285 
Nitroamines,  137,  165 
Nitroamido-o-benzyl  alcohol,  170 
Nitroacetanilide,  178 
Nitroacetophenone,  183 
Nitroacid-nitriles,  166 
Nitroanisol,  165,  175,  176 
Nitroanthraquinone,  191,  210 
Nitrobenzaldehyde,  169,  172,  181, 

188 
Nitrobenzene : 

(1)  General  observations,  135-145 

(2)  Reduction  of,  145-163 

(3)  Substitution  products,  163-167, 

184,189,257 

(4)  —  and  nitrogen,  285 
Nitrobenzeneazonaphthol,  190 
Nitrobenzeneazophenol,  190 
Nitrobenzeneazosalicylic  acid,  190 
Nitrobenzenecarboxylic  acid,  166 
Nitrobenzenesulphonic    acids,     156, 

183,  186,  189 

Nitrobenzoic  acids,  172, 183, 188, 189 
Nitrobenzoic  esters,  184 


Nitrobenzonitriles,  186 

Nitrobenzophenone,  183 

Nitrobenzyl  alcohol,  168,  171 

Nitrobenzylaniline,  172 

Nitrobenzylidenealdehydophenylhy- 
droxylamines,  182 

Nitro-bitter-almond-oil-green,  181 

Nitrocarboxylic  acids,  137 

Nitrocinnamic  acids,  185 

Nitro-compounds,  aromatic,  135-193 

Nitrocumic  esters,  185 

Nitrocyanacetamide,  109 

Nitro-derivatives,  56 

Nitrodiamidotolylmethane,  181 

Nitrodiamidotriphenylmethane,  181 

Nitrodiethylaniline,  179 

Nitrodimethylaniline,  177,  178 

Nitrodimethyltoluidine,  179 

Nitrodiphenyl,  173 

Nitrodiphenylamine,  180 

Nitroethane,  57 

Nitroethane  and  nitrogen,  285 

Nitrogen,  246,  251 

Nitrogen  and  water,  270 

Nitrogen  and  carbon  monoxide,  268, 
270 

Nitrogen  and  hydrocarbons,  271-273 

Nitrogen,  binding  of,  to  organic  sub- 
stances, 279 

Nitrogen   compounds  and   nitrogen, 
284 

Nitrohydroquinone,  133 

Nitroketones,  181 

Nitroleuco-bodies,  181 

Nitroleucomalachite  green,  172 

Nitromalonamide,  109 

Ntromalonic  acid,  109 

Nitromethane,  56 

Nitromethane  and  nitrogen,  285 

Nitromethylaniline,  178 

Nitronaphthalene,  190 

Nitronaphthalenesulphonic  acid,  191 

Nitronaphthylamine,  190 

Nitronaphthyl  ethyl  ether,  191 

Nitrooxyanthraquinone,  191,  210 

Nitrophenanthrene,  192 

Nitrophenanthrenequinone,  192 

Nitrophenetol,  176 

Nitrophenols,  133,  136,  166,  175,  176 

Nitrophenyl  ethers,  177 

Nitrotolyl  ether,  177 

Nitrophenyltolylketone,  183 

Nitrophthalic  acids,  186 

Nitropropane,  57 

Nitroprusside,  sodium,  127 

Nitroquinoline,  193 

Nitrosoaldehydecopellidine,  193 

Nitrosobenzene,  135-163 

Nitroso-compounds,  134-163 

Nitrosodiethylaniline,  179 


INDEX. 


305 


Nitrosodimethylaniline,  178 
Nitrosolupetidine,  193 
Nitrosopipecplines,  192,  193 
Nitrosopiperidine,  192 
Nitrosostyrol,  190 
Nitrosotetrahydroquinoline,  1 93 
Nitrosotrimethylpiperidine,  193 
Nitrotetraethyldiamidotriphenylme- 

thane,  181 
Nitrotetramethyldiamidotriphenyl- 

methane,  181 
Nitrotoluenes,  136, 141, 164, 168-172, 

189,  258 
Nitrotoluenesulphonic  acids,  173, 186, 

187 

Nitrotoluic  acid,  185 
Nitrotoluidines,  179 
Nitrotoluquinolines,  150,  193 
Nitrotolylamidophenylmethane,  1 72 
Nitroxylenes,  172 
Nosophen,  201 

Octane,  90,  95 

Octandion,  100,  102 

Octodecandi-acid,  115 

(Enanthylic  acid,  93 

Olefines,  93 

Oleic  acid,  94 

Opium,  220 

Orange  II,  198 

Osmotic  pressure,  electrolytic,  26 

Osmotic  theory,  26 

Oxalic  acid,  65,  104,  110,  231,  232, 

279 

Oxalic  esters,  105 
Oximes,  203 
Oxy-acids,  96 

Oxyamidoisophthalic  acid,  186 
Oxyamidoquinoline,  193 
Oxyanthranol,  210 
Oxyanthraquinones,  210 
Oxyanthranilic  acid,  184 
Oxybenzoic  acids,  214 
Oxybenzoic  acids  and  nitrogen,  284 
Oxybenzophenone,  207 
Oxybenzophenone-benzoate,  207 
Oxybenzpinacone,  207 
Oxybenzyl  alcohol,  203 
Oxybutyric  acids,  98,  99 
Oxycarbostyril,  185 
Oxycarboxylic  acids,  214 
Oxycaproic  acid,  232 
Oxydihydropurin,  128 
Oxydimorphine  sulphate,  220 
Oxyphenanthrenequinones,  210 
Oxypropionic  acids,  97 
Oxypurins,  128,  130 
Oxytrimethylene  urea,  123 
Oxypyronedicarboxylic  acid,  220 
Ozonizers,  263 


Parabanic  acid,  122,  168 
Paraldehyde,  276 
Paraldehyde  and  nitrogen,  283 
Peat,  233 

Pelargonic  acid,  93 
Pentenecarboxylic  ethyl  ester,  114 
Perbrombenzene,  256 
Perbrommethylene,  253 
Percarbonic  acid,  77 
Perchlorbenzene,  253,  254,  255 
Perchlorethane,  253,  254,  255 
Perchlorethylene,  250,  253,  254,  255 
Persulphide,  acetyl,  85 
Petroleum,  250 
Phenanthrenequinone,  210 
Phenazpne,  173 
Phenetidine,  176 
Phenol,  199,  20!,  231,  232,  276 
Phenol  and  nitrogen,  281 
Phenolphthalein,  201 
Phenols,  199 
Phenomorpholone,  223 
Phenose,  134 
Phentriazole,  189,  190 
Phenylacetic  acid,  213,  215 
Phenylacetic  ester,  78 
Phenylchloramine,  157 
Phenyldisulphide,  201 
Phenylenediamine,  164, 167, 177, 178, 

19o,  285 

Phenylethylamine,  204,  216 
Phenylglyceric  acid,  215 
Phenylhydrazine  and  nitrogen,  285 
Phenylhydrazones,  67,  203 
Phenylhydroxylamine,  138-146-155- 

163 

Phenylisocyanide,  163,  254 
Phenyllactic  acid,  215 
Phenylmercaptan,  201 
Phenylmethylene,  259 
Phenylnaphthylcarbinol,  206 
Phenylnaphthylketone,  206 
Phenylnaphthylpinacone,  206 
Phenylpyrrolidone,  119,  215    - 
Phenylsulphocarbazinic  acid,  131 
Phenylsulphuric  acid,  230 
Phenyltolylamine,  195 
Phenyltolylcarbinol,  206 
Phenyltolylketone,  206 
Phenyltolylpinacone,  206 
Phenylxylylcarbinol,  206 
Phenylxylylketone,  206 
Phenylxylylpinacone,  206 
Phorone,  70 
Phosgene,  255,  256 
Phthalic  acid,  116,  134,212 
Phthalic  ester,  212,  213 
Phthalylaminobenzophenone,  207 
Picoline,  218 
Picramic  acid,  176 


306 


INDEX. 


Picric  acid,  176,  199 

Pimelic  acid,  114 

Pinacolines,  207 

Pinacones,  70,  207 

Pipecoline,  192,  218 

Pipecolylhydrazine,  193 

Piperidine,  192,  218 

Piperidine  and  nitrogen,  285 

Piperylhydrazine,  192 

Pivalic  acid,  92 

Polyamines,  283 

Polybasic  acids,  116 

Potassium  acetate,  95,  97,  101,  108, 

111,  214 

Potassium  butyrates,  88, 101, 108,  214 
Potassium  caprcate,  93,  214 
Potassium  cyanacetate,  85 
Potassium  cyanate,  120 
Potassium  cyanide,  120 
Potassium  ethyl-carbonate,  59 
Potassium  ethyl  malonate,  108 
Potassium  ethyl  succinate,  111 
Potassium  ethylthiocarbonate,  131 
Potassium  ferricyanide,  120 
Potassium  ferrocyanide,  120 
Potassium  glycollate,  97 
Potassium  heptylate,  93 
Potassium  isethionate,  66 
Potassium  isoamyl-phosphate,  66 
Potassium  isoamyl-sulphate,  66 
Potassium  isoamylxanthate,  131 
Potassium  isobutylxanthate,  131 
Potassium  isobutyrate,  112 
Potassium  lanvulinate   100,  102 
Potassium  methyl-carbonate,  58 
Potassium  methylxanthate,  131 
Potassium  oenanthylate,  95 
Potassium  percarbonate,  77 
Potassium  phenylsulphocarbazinate, 

131 

Potassium  propionate,  86,  108" 
Potassium  pyroracemate,  100,  101 
Potassium  succinate,  110 
Potassium  trichlormethylsulphonate, 

65 

Potassium  valerate,  95 
Potassium  xanthate,  6,  131 
Potential  difference,  44 
Potential,  electrode,  14 
Potential,  excess,  20 
Propionic  acid,  63,  64,  86,  100,  279 
Propionic  acid  and  nitrogen,  284 
Propionic  aldehyde,  63,  89,  98,  114, 

279 

Propionic  aldehyde  and  nitrogen,  282 
Propionic  esters,  108 
Propyl  alcohols,  63,  88,  89,  113,  114, 

276 

Propyl  alcohols  and  nitrogen,  280 
Propylamine,  57,  121,  284 


Propylbenzene,  214 
Propyl  butyrate,  89 
Propylene,  88,  113,  114,  271 
Propylene  and  nitrogen,  271 
Propylene  bromide,  88 
Propylenediamine  and  nitrogen,  285 
Propylene  oxide,  114 
Propylhydrocinnamic  ester,  244 
Propylhydroxylamine,  57 
Propylnitrile,  121 
Propylpseudonitrole,  73 
Prussian  blue,  120 
Pseudocumene,  134 
Pseudonitroles,  72 
Pseudotropine,  219,  220 
Purins,  122 
Purons,  125,  126 
Purpurin,  210 
Purpurogallin,  202 
Purpurogallincarboxylic  acid,  202 
Pyrazolidine,  74 
Pyridine,  218,  285 
Pyridine  derivatives,  21 7 
Pyrocatechin,  231 
Pyrogallol,  202 
Pyrogallol  and  nitrogen,  282 
Pyrometers,  239 
Pyroracemic  acid,  100,  101,  102 
Pyroracemic  acid  and  nitrogen,  284 
Pyrotartaric  acid,  113 
Pyrrol  and  nitrogen,  285 
Pyrrolidone,  119 

Quinaldine,  219 

Quinhydrone,  133 

Quinia  bases,  221 

Quinine,  221 

Quinizarin,  210 

Quinone,  133,  164,  165,  177,  180,  194, 

201 

Quinone  and  nitrogen,  283 
Quinonediimide,  164 
Quinonehydrone,  202 

Racemic  acid,  117 
Reaction  temperatures,  238 
Reaction  velocity,  1 1 ,  30 
Resorcin,  201,  202 
Resorcin  and  nitrogen,  281 
Rocceline,  198 
Rosaniline,  181,  195 

Saccharic  acid,  68 
Saccharic  aldehyde,  65,  203 
Saccharin,  216 
Safranine,  195 
Salicin,  203 
Salicyl  alcohol,  203 
Salicylaldehydephenylhydrazone,  204 
Salicyl- a-osazone,  204 


INDEX. 


307 


Salicylic  acid,  133,  201,  214,  258   >    - 
Salicylic-acid-phentriazole,  110 
Salicylic  aldehyde,  283 
Salicylosazone,  204 
Saligenin,  203 

Saligenin-glucose,  see  Salicin 
Saliretin,  203 
Sandmeyer-Gattermann     reaction, 

electrolytic,  196 
Sarcine,  127 
Sarcolactic  acid,  98 
Sebasic  acid,  115 
Sebasic  diethyl  ester,  114,  115 
Short-circuiting  cells,  50,  180 
Silent  electric  discharge,  235,  261 
Sodium  acetoacetic  ester,  100 
Sodium  dichloracetate,  85 
Sodium  dichlorpropionate,  87 
Sodium  formate,  81 
Sodium  glycollate,  97 
Sodium  iodopropionate,  87 
Sodium  malonic  diethyl  ester,  108 
Sodium  nitroprusside,  120 
Sodium  propionate,  86,  111 
Sodium  succinate,  111 
Spark  discharge,  244 
Standard  electrodes,  45 
Stilbene,  259 
Strychnidine,  222 
Strychnine,  221 
Strychnos  bases,  221 
Suberic  acid,  113,  115 
Substances  reducible  with  difficulty, 

23 

Succinanil,  119,  215 
Succinic  acid,  109,  115,  231,  232 
Succinic  diethyl  ester,  103,  112 
Succinimide,  119 
Sugar,  268 
Sugar-juice  purification,  electrolytic, 

69 

Sulphoanthranilic  acid,  214 
Sulphoazobenzoic  acid,  189 
Sulphobenzoic  acid,  134,  212,  213 
Sulphocarbamide,  285 
"Sun  yellow,"  173,  187 

Tannic  acid,  202 
Tannic,  214 
Tanning,  electric,  234 
Tartaric  acid,  110,  116 
Tartaric  acid  and  nitrogen,  284 
Tartronyl  urea,  123 
Terephthalic  acid,  213 
Tesla  currents,  261,  288 
Tetracetylethane,  74 
Tetrachlorhexyleneglycol,  90 
Tetrachlormethane,  255 
Tetradecane,  93 
Tetraethylammonium  chloride,  118 


Tetraethylammomum  triiodide,  118 

Tetraethyldiaminophenazone,  174 

Tetraethylthiuramdisulphide,  131 

Tetrahydrobrucine,  222 

Tetrahydroquinaldine,  219 

Tetrahydroquinoline,  193 

Tetrahydrostrychnine,  222 

Tetrahydrouric  acid,  125 

Tetraiodophenolphthalem,  201 

Tetramethylammonium  hydrate,  118 

Tetramethylbenzidine,  198 

Tetramethyldiamidoazobenzene,  1 77 

Tetramethyldiamid9azotoluene,  180 

Tetramethyldiamidobenzophenone. 
207 

Tetramethyldiamidodiphenylmeth- 
ane,  208 

Tetramethyldiamidohydrazotoluene, 
180 

Tetramethyldiamidophenazone,  174 

Tetramethyldiamidophenazone      ox- 
ide, 174 

Tetramethylpuron,  127 

Tetramethylsuccinic  acid,  107 

Tetramethyluric  acid,  127 

Tetraphenylerythrite,  209 

Tetraoxyazobenzene,  133 

Tetraoxydibromanthraquinone,  210 

Thalleioquin,  221 

Theobromine,  127,  129 

Theoretics,  6,  235 

Thioacetic  acid,  85 

Thiobenzoic  acid,  212 

Thiocarbonic  acid  derivatives,  130 

Thioformaldehyde,  269 

Thiophene,  286 

Thiuramdisulphide,  131 

Thymol,  200 

Tolane  chlorides,  259 

Tolidine,  168 

Toluene,  134,  249 

Toluenesulphamide,  216 

Toluenesulphonamide,  216 

Toluenesulphonic  acid,  213 

Toluic  acid,  213 

Toluic  aldehydes,  134 

Toluidine,  136,  140,  167,  169,  170, 
195 

Toluidines  and  nitrogen,  285 

Tolunitrile  and  nitrogen,  285 

Toluylenediamine,  179 

Tolylpyrrolidone,  120 

Tolylsuccinimide,  120 

Triamidotriphenylme  thane,  199 

Tribromhydrin,  248 

Tricarballylic  acid,  117,  118 

Trichloracetic  acid,  85,  256 

Trichloracetic    trichlormethyl    ester, 
85 

Trichlorbutyrate,  90 


308 


INDEX. 


Trichlorbutyric  acid,  90 
Trimethylacetic  acid,  92 
Trimethylamine,  248 
Trimethylamine  and  nitrogen,  284 
Trimethylcarbinol,  91,  92 
Trimethylene,  271 
Trimethylenetritoluidine,  170,  171 
Trimethylene  urea,  123 
Trimethylethylene,  253 
Trimethylisopuron,  127 
Trimethylmethyl  isovalerate,  91 
Trimethyloxydihydropuron,  1 29 
Trimethylpiperylhydrazine,  193 
Trimethylpuron,  127 
Trimethyluric  acid,  127 
Trimethylxanthine,  129 
Trinitrobenzoic  acid,  173 
Trinitrophenol,  176 
Trinitrotoluene,  173 
Trioxyanthraquinone,  210 
Triphenylguanidine,  254 
Triphenylmethane  dyes,  199 
Trioxymethylene,  64,  65,  68,  253 
Trioxymethylene  and  nitrogen,  283 
Tropic  acid,  219 
Tropine,  219,  220 


Tropinone,  219,  220 
Turpentine,  273 

Unattackable  electrodes,  18 

Undecylenic  acid,  94 

Unsaturated  acicls,  115 

Unsaturated  esters,  108 

Uramil,  124 

Urea,  270 

Uric  acid,  122,  125 

Valeric  acids,  90,  92,  231,  232 

Valeric  ethyl  ester,  108,  111 

Vanillin,  202 

Vapors  and  Tesla  currents,  288 

Velocity  of  reaction,  11,  13 

Viol  uric  acid,  124 

Voltaic  arc,  244,  249 

Xanthates,  see  Potassium  xanthate 
Xanthate,  potassium,  131 
Xanthic  disulphide,  6 
Xanthic  supersulphide,  131 
Xanthine,  127 
Xylenes,  134 


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